/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.tools.picocli;

import java.io.File;
import java.io.PrintStream;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.net.InetAddress;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.charset.Charset;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.sql.Time;
import java.text.BreakIterator;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.SortedSet;
import java.util.Stack;
import java.util.TreeSet;
import java.util.UUID;
import java.util.concurrent.Callable;
import java.util.regex.Pattern;

import org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Ansi.IStyle;
import org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Ansi.Style;
import org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Ansi.Text;

import static java.util.Locale.ENGLISH;
import static org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Column.Overflow.SPAN;
import static org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Column.Overflow.TRUNCATE;
import static org.apache.logging.log4j.core.tools.picocli.CommandLine.Help.Column.Overflow.WRAP;

/**
 * <p>
 * CommandLine interpreter that uses reflection to initialize an annotated domain object with values obtained from the
 * command line arguments.
 * </p><h2>Example</h2>
 * <pre>import static picocli.CommandLine.*;
 *
 * &#064;Command(header = "Encrypt FILE(s), or standard input, to standard output or to the output file.",
 *          version = "v1.2.3")
 * public class Encrypt {
 *
 *     &#064;Parameters(type = File.class, description = "Any number of input files")
 *     private List&lt;File&gt; files = new ArrayList&lt;File&gt;();
 *
 *     &#064;Option(names = { "-o", "--out" }, description = "Output file (default: print to console)")
 *     private File outputFile;
 *
 *     &#064;Option(names = { "-v", "--verbose"}, description = "Verbosely list files processed")
 *     private boolean verbose;
 *
 *     &#064;Option(names = { "-h", "--help", "-?", "-help"}, usageHelp = true, description = "Display this help and exit")
 *     private boolean help;
 *
 *     &#064;Option(names = { "-V", "--version"}, versionHelp = true, description = "Display version info and exit")
 *     private boolean versionHelp;
 * }
 * </pre>
 * <p>
 * Use {@code CommandLine} to initialize a domain object as follows:
 * </p><pre>
 * public static void main(String... args) {
 *     Encrypt encrypt = new Encrypt();
 *     try {
 *         List&lt;CommandLine&gt; parsedCommands = new CommandLine(encrypt).parse(args);
 *         if (!CommandLine.printHelpIfRequested(parsedCommands, System.err, Help.Ansi.AUTO)) {
 *             runProgram(encrypt);
 *         }
 *     } catch (ParameterException ex) { // command line arguments could not be parsed
 *         System.err.println(ex.getMessage());
 *         ex.getCommandLine().usage(System.err);
 *     }
 * }
 * </pre><p>
 * Invoke the above program with some command line arguments. The below are all equivalent:
 * </p>
 * <pre>
 * --verbose --out=outfile in1 in2
 * --verbose --out outfile in1 in2
 * -v --out=outfile in1 in2
 * -v -o outfile in1 in2
 * -v -o=outfile in1 in2
 * -vo outfile in1 in2
 * -vo=outfile in1 in2
 * -v -ooutfile in1 in2
 * -vooutfile in1 in2
 * </pre>
 */
public class CommandLine {
    /** This is picocli version {@value}. */
    public static final String VERSION = "2.0.3";

    private final Tracer tracer = new Tracer();
    private final Interpreter interpreter;
    private String commandName = Help.DEFAULT_COMMAND_NAME;
    private boolean overwrittenOptionsAllowed = false;
    private boolean unmatchedArgumentsAllowed = false;
    private final List<String> unmatchedArguments = new ArrayList<>();
    private CommandLine parent;
    private boolean usageHelpRequested;
    private boolean versionHelpRequested;
    private final List<String> versionLines = new ArrayList<>();

    /**
     * Constructs a new {@code CommandLine} interpreter with the specified annotated object.
     * When the {@link #parse(String...)} method is called, fields of the specified object that are annotated
     * with {@code @Option} or {@code @Parameters} will be initialized based on command line arguments.
     * @param command the object to initialize from the command line arguments
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     */
    public CommandLine(final Object command) {
        interpreter = new Interpreter(command);
    }

    /** Registers a subcommand with the specified name. For example:
     * <pre>
     * CommandLine commandLine = new CommandLine(new Git())
     *         .addSubcommand("status",   new GitStatus())
     *         .addSubcommand("commit",   new GitCommit();
     *         .addSubcommand("add",      new GitAdd())
     *         .addSubcommand("branch",   new GitBranch())
     *         .addSubcommand("checkout", new GitCheckout())
     *         //...
     *         ;
     * </pre>
     *
     * <p>The specified object can be an annotated object or a
     * {@code CommandLine} instance with its own nested subcommands. For example:</p>
     * <pre>
     * CommandLine commandLine = new CommandLine(new MainCommand())
     *         .addSubcommand("cmd1",                 new ChildCommand1()) // subcommand
     *         .addSubcommand("cmd2",                 new ChildCommand2())
     *         .addSubcommand("cmd3", new CommandLine(new ChildCommand3()) // subcommand with nested sub-subcommands
     *                 .addSubcommand("cmd3sub1",                 new GrandChild3Command1())
     *                 .addSubcommand("cmd3sub2",                 new GrandChild3Command2())
     *                 .addSubcommand("cmd3sub3", new CommandLine(new GrandChild3Command3()) // deeper nesting
     *                         .addSubcommand("cmd3sub3sub1", new GreatGrandChild3Command3_1())
     *                         .addSubcommand("cmd3sub3sub2", new GreatGrandChild3Command3_2())
     *                 )
     *         );
     * </pre>
     * <p>The default type converters are available on all subcommands and nested sub-subcommands, but custom type
     * converters are registered only with the subcommand hierarchy as it existed when the custom type was registered.
     * To ensure a custom type converter is available to all subcommands, register the type converter last, after
     * adding subcommands.</p>
     * <p>See also the {@link Command#subcommands()} annotation to register subcommands declaratively.</p>
     *
     * @param name the string to recognize on the command line as a subcommand
     * @param command the object to initialize with command line arguments following the subcommand name.
     *          This may be a {@code CommandLine} instance with its own (nested) subcommands
     * @return this CommandLine object, to allow method chaining
     * @see #registerConverter(Class, ITypeConverter)
     * @since 0.9.7
     * @see Command#subcommands()
     */
    public CommandLine addSubcommand(final String name, final Object command) {
        final CommandLine commandLine = toCommandLine(command);
        commandLine.parent = this;
        interpreter.commands.put(name, commandLine);
        return this;
    }
    /** Returns a map with the subcommands {@linkplain #addSubcommand(String, Object) registered} on this instance.
     * @return a map with the registered subcommands
     * @since 0.9.7
     */
    public Map<String, CommandLine> getSubcommands() {
        return new LinkedHashMap<>(interpreter.commands);
    }
    /**
     * Returns the command that this is a subcommand of, or {@code null} if this is a top-level command.
     * @return the command that this is a subcommand of, or {@code null} if this is a top-level command
     * @see #addSubcommand(String, Object)
     * @see Command#subcommands()
     * @since 0.9.8
     */
    public CommandLine getParent() {
        return parent;
    }

    /** Returns the annotated object that this {@code CommandLine} instance was constructed with.
     * @param <T> the type of the variable that the return value is being assigned to
     * @return the annotated object that this {@code CommandLine} instance was constructed with
     * @since 0.9.7
     */
    public <T> T getCommand() {
        return (T) interpreter.command;
    }

    /** Returns {@code true} if an option annotated with {@link Option#usageHelp()} was specified on the command line.
     * @return whether the parser encountered an option annotated with {@link Option#usageHelp()}.
     * @since 0.9.8 */
    public boolean isUsageHelpRequested() { return usageHelpRequested; }

    /** Returns {@code true} if an option annotated with {@link Option#versionHelp()} was specified on the command line.
     * @return whether the parser encountered an option annotated with {@link Option#versionHelp()}.
     * @since 0.9.8 */
    public boolean isVersionHelpRequested() { return versionHelpRequested; }

    /** Returns whether options for single-value fields can be specified multiple times on the command line.
     * The default is {@code false} and a {@link OverwrittenOptionException} is thrown if this happens.
     * When {@code true}, the last specified value is retained.
     * @return {@code true} if options for single-value fields can be specified multiple times on the command line, {@code false} otherwise
     * @since 0.9.7
     */
    public boolean isOverwrittenOptionsAllowed() {
        return overwrittenOptionsAllowed;
    }

    /** Sets whether options for single-value fields can be specified multiple times on the command line without a {@link OverwrittenOptionException} being thrown.
     * <p>The specified setting will be registered with this {@code CommandLine} and the full hierarchy of its
     * subcommands and nested sub-subcommands <em>at the moment this method is called</em>. Subcommands added
     * later will have the default setting. To ensure a setting is applied to all
     * subcommands, call the setter last, after adding subcommands.</p>
     * @param newValue the new setting
     * @return this {@code CommandLine} object, to allow method chaining
     * @since 0.9.7
     */
    public CommandLine setOverwrittenOptionsAllowed(final boolean newValue) {
        this.overwrittenOptionsAllowed = newValue;
        for (final CommandLine command : interpreter.commands.values()) {
            command.setOverwrittenOptionsAllowed(newValue);
        }
        return this;
    }

    /** Returns whether the end user may specify arguments on the command line that are not matched to any option or parameter fields.
     * The default is {@code false} and a {@link UnmatchedArgumentException} is thrown if this happens.
     * When {@code true}, the last unmatched arguments are available via the {@link #getUnmatchedArguments()} method.
     * @return {@code true} if the end use may specify unmatched arguments on the command line, {@code false} otherwise
     * @see #getUnmatchedArguments()
     * @since 0.9.7
     */
    public boolean isUnmatchedArgumentsAllowed() {
        return unmatchedArgumentsAllowed;
    }

    /** Sets whether the end user may specify unmatched arguments on the command line without a {@link UnmatchedArgumentException} being thrown.
     * <p>The specified setting will be registered with this {@code CommandLine} and the full hierarchy of its
     * subcommands and nested sub-subcommands <em>at the moment this method is called</em>. Subcommands added
     * later will have the default setting. To ensure a setting is applied to all
     * subcommands, call the setter last, after adding subcommands.</p>
     * @param newValue the new setting. When {@code true}, the last unmatched arguments are available via the {@link #getUnmatchedArguments()} method.
     * @return this {@code CommandLine} object, to allow method chaining
     * @since 0.9.7
     * @see #getUnmatchedArguments()
     */
    public CommandLine setUnmatchedArgumentsAllowed(final boolean newValue) {
        this.unmatchedArgumentsAllowed = newValue;
        for (final CommandLine command : interpreter.commands.values()) {
            command.setUnmatchedArgumentsAllowed(newValue);
        }
        return this;
    }

    /** Returns the list of unmatched command line arguments, if any.
     * @return the list of unmatched command line arguments or an empty list
     * @see #isUnmatchedArgumentsAllowed()
     * @since 0.9.7
     */
    public List<String> getUnmatchedArguments() {
        return unmatchedArguments;
    }

    /**
     * <p>
     * Convenience method that initializes the specified annotated object from the specified command line arguments.
     * </p><p>
     * This is equivalent to
     * </p><pre>
     * CommandLine cli = new CommandLine(command);
     * cli.parse(args);
     * return command;
     * </pre>
     *
     * @param command the object to initialize. This object contains fields annotated with
     *          {@code @Option} or {@code @Parameters}.
     * @param args the command line arguments to parse
     * @param <T> the type of the annotated object
     * @return the specified annotated object
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     * @throws ParameterException if the specified command line arguments are invalid
     * @since 0.9.7
     */
    public static <T> T populateCommand(final T command, final String... args) {
        final CommandLine cli = toCommandLine(command);
        cli.parse(args);
        return command;
    }

    /** Parses the specified command line arguments and returns a list of {@code CommandLine} objects representing the
     * top-level command and any subcommands (if any) that were recognized and initialized during the parsing process.
     * <p>
     * If parsing succeeds, the first element in the returned list is always {@code this CommandLine} object. The
     * returned list may contain more elements if subcommands were {@linkplain #addSubcommand(String, Object) registered}
     * and these subcommands were initialized by matching command line arguments. If parsing fails, a
     * {@link ParameterException} is thrown.
     * </p>
     *
     * @param args the command line arguments to parse
     * @return a list with the top-level command and any subcommands initialized by this method
     * @throws ParameterException if the specified command line arguments are invalid; use
     *      {@link ParameterException#getCommandLine()} to get the command or subcommand whose user input was invalid
     */
    public List<CommandLine> parse(final String... args) {
        return interpreter.parse(args);
    }
    /**
     * Represents a function that can process a List of {@code CommandLine} objects resulting from successfully
     * {@linkplain #parse(String...) parsing} the command line arguments. This is a
     * <a href="https://docs.oracle.com/javase/8/docs/api/java/util/function/package-summary.html">functional interface</a>
     * whose functional method is {@link #handleParseResult(List, PrintStream, CommandLine.Help.Ansi)}.
     * <p>
     * Implementations of this functions can be passed to the {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...) CommandLine::parseWithHandler}
     * methods to take some next step after the command line was successfully parsed.
     * </p>
     * @see RunFirst
     * @see RunLast
     * @see RunAll
     * @since 2.0 */
    public static interface IParseResultHandler {
        /** Processes a List of {@code CommandLine} objects resulting from successfully
         * {@linkplain #parse(String...) parsing} the command line arguments and optionally returns a list of results.
         * @param parsedCommands the {@code CommandLine} objects that resulted from successfully parsing the command line arguments
         * @param out the {@code PrintStream} to print help to if requested
         * @param ansi for printing help messages using ANSI styles and colors
         * @return a list of results, or an empty list if there are no results
         * @throws ExecutionException if a problem occurred while processing the parse results; use
         *      {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
         */
        List<Object> handleParseResult(List<CommandLine> parsedCommands, PrintStream out, Help.Ansi ansi) throws ExecutionException;
    }
    /**
     * Represents a function that can handle a {@code ParameterException} that occurred while
     * {@linkplain #parse(String...) parsing} the command line arguments. This is a
     * <a href="https://docs.oracle.com/javase/8/docs/api/java/util/function/package-summary.html">functional interface</a>
     * whose functional method is {@link #handleException(CommandLine.ParameterException, PrintStream, CommandLine.Help.Ansi, String...)}.
     * <p>
     * Implementations of this functions can be passed to the {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...) CommandLine::parseWithHandler}
     * methods to handle situations when the command line could not be parsed.
     * </p>
     * @see DefaultExceptionHandler
     * @since 2.0 */
    public static interface IExceptionHandler {
        /** Handles a {@code ParameterException} that occurred while {@linkplain #parse(String...) parsing} the command
         * line arguments and optionally returns a list of results.
         * @param ex the ParameterException describing the problem that occurred while parsing the command line arguments,
         *           and the CommandLine representing the command or subcommand whose input was invalid
         * @param out the {@code PrintStream} to print help to if requested
         * @param ansi for printing help messages using ANSI styles and colors
         * @param args the command line arguments that could not be parsed
         * @return a list of results, or an empty list if there are no results
         */
        List<Object> handleException(ParameterException ex, PrintStream out, Help.Ansi ansi, String... args);
    }
    /**
     * Default exception handler that prints the exception message to the specified {@code PrintStream}, followed by the
     * usage message for the command or subcommand whose input was invalid.
     * <p>Implementation roughly looks like this:</p>
     * <pre>
     *     System.err.println(paramException.getMessage());
     *     paramException.getCommandLine().usage(System.err);
     * </pre>
     * @since 2.0 */
    public static class DefaultExceptionHandler implements IExceptionHandler {
        @Override
        public List<Object> handleException(final ParameterException ex, final PrintStream out, final Help.Ansi ansi, final String... args) {
            out.println(ex.getMessage());
            ex.getCommandLine().usage(out, ansi);
            return Collections.emptyList();
        }
    }
    /**
     * Helper method that may be useful when processing the list of {@code CommandLine} objects that result from successfully
     * {@linkplain #parse(String...) parsing} command line arguments. This method prints out
     * {@linkplain #usage(PrintStream, Help.Ansi) usage help} if {@linkplain #isUsageHelpRequested() requested}
     * or {@linkplain #printVersionHelp(PrintStream, Help.Ansi) version help} if {@linkplain #isVersionHelpRequested() requested}
     * and returns {@code true}. Otherwise, if none of the specified {@code CommandLine} objects have help requested,
     * this method returns {@code false}.
     * <p>
     * Note that this method <em>only</em> looks at the {@link Option#usageHelp() usageHelp} and
     * {@link Option#versionHelp() versionHelp} attributes. The {@link Option#help() help} attribute is ignored.
     * </p>
     * @param parsedCommands the list of {@code CommandLine} objects to check if help was requested
     * @param out the {@code PrintStream} to print help to if requested
     * @param ansi for printing help messages using ANSI styles and colors
     * @return {@code true} if help was printed, {@code false} otherwise
     * @since 2.0 */
    public static boolean printHelpIfRequested(final List<CommandLine> parsedCommands, final PrintStream out, final Help.Ansi ansi) {
        for (final CommandLine parsed : parsedCommands) {
            if (parsed.isUsageHelpRequested()) {
                parsed.usage(out, ansi);
                return true;
            } else if (parsed.isVersionHelpRequested()) {
                parsed.printVersionHelp(out, ansi);
                return true;
            }
        }
        return false;
    }
    private static Object execute(final CommandLine parsed) {
        final Object command = parsed.getCommand();
        if (command instanceof Runnable) {
            try {
                ((Runnable) command).run();
                return null;
            } catch (final Exception ex) {
                throw new ExecutionException(parsed, "Error while running command (" + command + ")", ex);
            }
        } else if (command instanceof Callable) {
            try {
                return ((Callable<Object>) command).call();
            } catch (final Exception ex) {
                throw new ExecutionException(parsed, "Error while calling command (" + command + ")", ex);
            }
        }
        throw new ExecutionException(parsed, "Parsed command (" + command + ") is not Runnable or Callable");
    }
    /**
     * Command line parse result handler that prints help if requested, and otherwise executes the top-level
     * {@code Runnable} or {@code Callable} command.
     * For use in the {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...) parseWithHandler} methods.
     * <p>
     * From picocli v2.0, {@code RunFirst} is used to implement the {@link #run(Runnable, PrintStream, Help.Ansi, String...) run}
     * and {@link #call(Callable, PrintStream, Help.Ansi, String...) call} convenience methods.
     * </p>
     * @since 2.0 */
    public static class RunFirst implements IParseResultHandler {
        /** Prints help if requested, and otherwise executes the top-level {@code Runnable} or {@code Callable} command.
         * If the top-level command does not implement either {@code Runnable} or {@code Callable}, a {@code ExecutionException}
         * is thrown detailing the problem and capturing the offending {@code CommandLine} object.
         *
         * @param parsedCommands the {@code CommandLine} objects that resulted from successfully parsing the command line arguments
         * @param out the {@code PrintStream} to print help to if requested
         * @param ansi for printing help messages using ANSI styles and colors
         * @return an empty list if help was requested, or a list containing a single element: the result of calling the
         *      {@code Callable}, or a {@code null} element if the top-level command was a {@code Runnable}
         * @throws ExecutionException if a problem occurred while processing the parse results; use
         *      {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
         */
        @Override
        public List<Object> handleParseResult(final List<CommandLine> parsedCommands, final PrintStream out, final Help.Ansi ansi) {
            if (printHelpIfRequested(parsedCommands, out, ansi)) { return Collections.emptyList(); }
            return Arrays.asList(execute(parsedCommands.get(0)));
        }
    }
    /**
     * Command line parse result handler that prints help if requested, and otherwise executes the most specific
     * {@code Runnable} or {@code Callable} subcommand.
     * For use in the {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...) parseWithHandler} methods.
     * <p>
     * Something like this:</p>
     * <pre>
     *     // RunLast implementation: print help if requested, otherwise execute the most specific subcommand
     *     if (CommandLine.printHelpIfRequested(parsedCommands, System.err, Help.Ansi.AUTO)) {
     *         return emptyList();
     *     }
     *     CommandLine last = parsedCommands.get(parsedCommands.size() - 1);
     *     Object command = last.getCommand();
     *     if (command instanceof Runnable) {
     *         try {
     *             ((Runnable) command).run();
     *         } catch (Exception ex) {
     *             throw new ExecutionException(last, "Error in runnable " + command, ex);
     *         }
     *     } else if (command instanceof Callable) {
     *         Object result;
     *         try {
     *             result = ((Callable) command).call();
     *         } catch (Exception ex) {
     *             throw new ExecutionException(last, "Error in callable " + command, ex);
     *         }
     *         // ...do something with result
     *     } else {
     *         throw new ExecutionException(last, "Parsed command (" + command + ") is not Runnable or Callable");
     *     }
     * </pre>
     * @since 2.0 */
    public static class RunLast implements IParseResultHandler {
        /** Prints help if requested, and otherwise executes the most specific {@code Runnable} or {@code Callable} subcommand.
         * If the last (sub)command does not implement either {@code Runnable} or {@code Callable}, a {@code ExecutionException}
         * is thrown detailing the problem and capturing the offending {@code CommandLine} object.
         *
         * @param parsedCommands the {@code CommandLine} objects that resulted from successfully parsing the command line arguments
         * @param out the {@code PrintStream} to print help to if requested
         * @param ansi for printing help messages using ANSI styles and colors
         * @return an empty list if help was requested, or a list containing a single element: the result of calling the
         *      {@code Callable}, or a {@code null} element if the last (sub)command was a {@code Runnable}
         * @throws ExecutionException if a problem occurred while processing the parse results; use
         *      {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
         */
        @Override
        public List<Object> handleParseResult(final List<CommandLine> parsedCommands, final PrintStream out, final Help.Ansi ansi) {
            if (printHelpIfRequested(parsedCommands, out, ansi)) { return Collections.emptyList(); }
            final CommandLine last = parsedCommands.get(parsedCommands.size() - 1);
            return Arrays.asList(execute(last));
        }
    }
    /**
     * Command line parse result handler that prints help if requested, and otherwise executes the top-level command and
     * all subcommands as {@code Runnable} or {@code Callable}.
     * For use in the {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...) parseWithHandler} methods.
     * @since 2.0 */
    public static class RunAll implements IParseResultHandler {
        /** Prints help if requested, and otherwise executes the top-level command and all subcommands as {@code Runnable}
         * or {@code Callable}. If any of the {@code CommandLine} commands does not implement either
         * {@code Runnable} or {@code Callable}, a {@code ExecutionException}
         * is thrown detailing the problem and capturing the offending {@code CommandLine} object.
         *
         * @param parsedCommands the {@code CommandLine} objects that resulted from successfully parsing the command line arguments
         * @param out the {@code PrintStream} to print help to if requested
         * @param ansi for printing help messages using ANSI styles and colors
         * @return an empty list if help was requested, or a list containing the result of executing all commands:
         *      the return values from calling the {@code Callable} commands, {@code null} elements for commands that implement {@code Runnable}
         * @throws ExecutionException if a problem occurred while processing the parse results; use
         *      {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
         */
        @Override
        public List<Object> handleParseResult(final List<CommandLine> parsedCommands, final PrintStream out, final Help.Ansi ansi) {
            if (printHelpIfRequested(parsedCommands, out, ansi)) {
                return null;
            }
            final List<Object> result = new ArrayList<>();
            for (final CommandLine parsed : parsedCommands) {
                result.add(execute(parsed));
            }
            return result;
        }
    }
    /**
     * Returns the result of calling {@link #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...)}
     * with {@code Help.Ansi.AUTO} and a new {@link DefaultExceptionHandler} in addition to the specified parse result handler,
     * {@code PrintStream}, and the specified command line arguments.
     * <p>
     * This is a convenience method intended to offer the same ease of use as the {@link #run(Runnable, PrintStream, Help.Ansi, String...) run}
     * and {@link #call(Callable, PrintStream, Help.Ansi, String...) call} methods, but with more flexibility and better
     * support for nested subcommands.
     * </p>
     * <p>Calling this method roughly expands to:</p>
     * <pre>
     * try {
     *     List&lt;CommandLine&gt; parsedCommands = parse(args);
     *     return parseResultsHandler.handleParseResult(parsedCommands, out, Help.Ansi.AUTO);
     * } catch (ParameterException ex) {
     *     return new DefaultExceptionHandler().handleException(ex, out, ansi, args);
     * }
     * </pre>
     * <p>
     * Picocli provides some default handlers that allow you to accomplish some common tasks with very little code.
     * The following handlers are available:</p>
     * <ul>
     *   <li>{@link RunLast} handler prints help if requested, and otherwise gets the last specified command or subcommand
     * and tries to execute it as a {@code Runnable} or {@code Callable}.</li>
     *   <li>{@link RunFirst} handler prints help if requested, and otherwise executes the top-level command as a {@code Runnable} or {@code Callable}.</li>
     *   <li>{@link RunAll} handler prints help if requested, and otherwise executes all recognized commands and subcommands as {@code Runnable} or {@code Callable} tasks.</li>
     *   <li>{@link DefaultExceptionHandler} prints the error message followed by usage help</li>
     * </ul>
     * @param handler the function that will process the result of successfully parsing the command line arguments
     * @param out the {@code PrintStream} to print help to if requested
     * @param args the command line arguments
     * @return a list of results, or an empty list if there are no results
     * @throws ExecutionException if the command line arguments were parsed successfully but a problem occurred while processing the
     *      parse results; use {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
     * @see RunLast
     * @see RunAll
     * @since 2.0 */
    public List<Object> parseWithHandler(final IParseResultHandler handler, final PrintStream out, final String... args) {
        return parseWithHandlers(handler, out, Help.Ansi.AUTO, new DefaultExceptionHandler(), args);
    }
    /**
     * Tries to {@linkplain #parse(String...) parse} the specified command line arguments, and if successful, delegates
     * the processing of the resulting list of {@code CommandLine} objects to the specified {@linkplain IParseResultHandler handler}.
     * If the command line arguments were invalid, the {@code ParameterException} thrown from the {@code parse} method
     * is caught and passed to the specified {@link IExceptionHandler}.
     * <p>
     * This is a convenience method intended to offer the same ease of use as the {@link #run(Runnable, PrintStream, Help.Ansi, String...) run}
     * and {@link #call(Callable, PrintStream, Help.Ansi, String...) call} methods, but with more flexibility and better
     * support for nested subcommands.
     * </p>
     * <p>Calling this method roughly expands to:</p>
     * <pre>
     * try {
     *     List&lt;CommandLine&gt; parsedCommands = parse(args);
     *     return parseResultsHandler.handleParseResult(parsedCommands, out, ansi);
     * } catch (ParameterException ex) {
     *     return new exceptionHandler.handleException(ex, out, ansi, args);
     * }
     * </pre>
     * <p>
     * Picocli provides some default handlers that allow you to accomplish some common tasks with very little code.
     * The following handlers are available:</p>
     * <ul>
     *   <li>{@link RunLast} handler prints help if requested, and otherwise gets the last specified command or subcommand
     * and tries to execute it as a {@code Runnable} or {@code Callable}.</li>
     *   <li>{@link RunFirst} handler prints help if requested, and otherwise executes the top-level command as a {@code Runnable} or {@code Callable}.</li>
     *   <li>{@link RunAll} handler prints help if requested, and otherwise executes all recognized commands and subcommands as {@code Runnable} or {@code Callable} tasks.</li>
     *   <li>{@link DefaultExceptionHandler} prints the error message followed by usage help</li>
     * </ul>
     *
     * @param handler the function that will process the result of successfully parsing the command line arguments
     * @param out the {@code PrintStream} to print help to if requested
     * @param ansi for printing help messages using ANSI styles and colors
     * @param exceptionHandler the function that can handle the {@code ParameterException} thrown when the command line arguments are invalid
     * @param args the command line arguments
     * @return a list of results produced by the {@code IParseResultHandler} or the {@code IExceptionHandler}, or an empty list if there are no results
     * @throws ExecutionException if the command line arguments were parsed successfully but a problem occurred while processing the parse
     *      result {@code CommandLine} objects; use {@link ExecutionException#getCommandLine()} to get the command or subcommand where processing failed
     * @see RunLast
     * @see RunAll
     * @see DefaultExceptionHandler
     * @since 2.0 */
    public List<Object> parseWithHandlers(final IParseResultHandler handler, final PrintStream out, final Help.Ansi ansi, final IExceptionHandler exceptionHandler, final String... args) {
        try {
            final List<CommandLine> result = parse(args);
            return handler.handleParseResult(result, out, ansi);
        } catch (final ParameterException ex) {
            return exceptionHandler.handleException(ex, out, ansi, args);
        }
    }
    /**
     * Equivalent to {@code new CommandLine(command).usage(out)}. See {@link #usage(PrintStream)} for details.
     * @param command the object annotated with {@link Command}, {@link Option} and {@link Parameters}
     * @param out the print stream to print the help message to
     * @throws IllegalArgumentException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     */
    public static void usage(final Object command, final PrintStream out) {
        toCommandLine(command).usage(out);
    }

    /**
     * Equivalent to {@code new CommandLine(command).usage(out, ansi)}.
     * See {@link #usage(PrintStream, Help.Ansi)} for details.
     * @param command the object annotated with {@link Command}, {@link Option} and {@link Parameters}
     * @param out the print stream to print the help message to
     * @param ansi whether the usage message should contain ANSI escape codes or not
     * @throws IllegalArgumentException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     */
    public static void usage(final Object command, final PrintStream out, final Help.Ansi ansi) {
        toCommandLine(command).usage(out, ansi);
    }

    /**
     * Equivalent to {@code new CommandLine(command).usage(out, colorScheme)}.
     * See {@link #usage(PrintStream, Help.ColorScheme)} for details.
     * @param command the object annotated with {@link Command}, {@link Option} and {@link Parameters}
     * @param out the print stream to print the help message to
     * @param colorScheme the {@code ColorScheme} defining the styles for options, parameters and commands when ANSI is enabled
     * @throws IllegalArgumentException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     */
    public static void usage(final Object command, final PrintStream out, final Help.ColorScheme colorScheme) {
        toCommandLine(command).usage(out, colorScheme);
    }

    /**
     * Delegates to {@link #usage(PrintStream, Help.Ansi)} with the {@linkplain Help.Ansi#AUTO platform default}.
     * @param out the printStream to print to
     * @see #usage(PrintStream, Help.ColorScheme)
     */
    public void usage(final PrintStream out) {
        usage(out, Help.Ansi.AUTO);
    }

    /**
     * Delegates to {@link #usage(PrintStream, Help.ColorScheme)} with the {@linkplain Help#defaultColorScheme(CommandLine.Help.Ansi) default color scheme}.
     * @param out the printStream to print to
     * @param ansi whether the usage message should include ANSI escape codes or not
     * @see #usage(PrintStream, Help.ColorScheme)
     */
    public void usage(final PrintStream out, final Help.Ansi ansi) {
        usage(out, Help.defaultColorScheme(ansi));
    }
    /**
     * Prints a usage help message for the annotated command class to the specified {@code PrintStream}.
     * Delegates construction of the usage help message to the {@link Help} inner class and is equivalent to:
     * <pre>
     * Help help = new Help(command).addAllSubcommands(getSubcommands());
     * StringBuilder sb = new StringBuilder()
     *         .append(help.headerHeading())
     *         .append(help.header())
     *         .append(help.synopsisHeading())      //e.g. Usage:
     *         .append(help.synopsis())             //e.g. &lt;main class&gt; [OPTIONS] &lt;command&gt; [COMMAND-OPTIONS] [ARGUMENTS]
     *         .append(help.descriptionHeading())   //e.g. %nDescription:%n%n
     *         .append(help.description())          //e.g. {"Converts foos to bars.", "Use options to control conversion mode."}
     *         .append(help.parameterListHeading()) //e.g. %nPositional parameters:%n%n
     *         .append(help.parameterList())        //e.g. [FILE...] the files to convert
     *         .append(help.optionListHeading())    //e.g. %nOptions:%n%n
     *         .append(help.optionList())           //e.g. -h, --help   displays this help and exits
     *         .append(help.commandListHeading())   //e.g. %nCommands:%n%n
     *         .append(help.commandList())          //e.g.    add       adds the frup to the frooble
     *         .append(help.footerHeading())
     *         .append(help.footer());
     * out.print(sb);
     * </pre>
     * <p>Annotate your class with {@link Command} to control many aspects of the usage help message, including
     * the program name, text of section headings and section contents, and some aspects of the auto-generated sections
     * of the usage help message.
     * <p>To customize the auto-generated sections of the usage help message, like how option details are displayed,
     * instantiate a {@link Help} object and use a {@link Help.TextTable} with more of fewer columns, a custom
     * {@linkplain Help.Layout layout}, and/or a custom option {@linkplain Help.IOptionRenderer renderer}
     * for ultimate control over which aspects of an Option or Field are displayed where.</p>
     * @param out the {@code PrintStream} to print the usage help message to
     * @param colorScheme the {@code ColorScheme} defining the styles for options, parameters and commands when ANSI is enabled
     */
    public void usage(final PrintStream out, final Help.ColorScheme colorScheme) {
        final Help help = new Help(interpreter.command, colorScheme).addAllSubcommands(getSubcommands());
        if (!Help.DEFAULT_SEPARATOR.equals(getSeparator())) {
            help.separator = getSeparator();
            help.parameterLabelRenderer = help.createDefaultParamLabelRenderer(); // update for new separator
        }
        if (!Help.DEFAULT_COMMAND_NAME.equals(getCommandName())) {
            help.commandName = getCommandName();
        }
        final StringBuilder sb = new StringBuilder()
                .append(help.headerHeading())
                .append(help.header())
                .append(help.synopsisHeading())      //e.g. Usage:
                .append(help.synopsis(help.synopsisHeadingLength())) //e.g. &lt;main class&gt; [OPTIONS] &lt;command&gt; [COMMAND-OPTIONS] [ARGUMENTS]
                .append(help.descriptionHeading())   //e.g. %nDescription:%n%n
                .append(help.description())          //e.g. {"Converts foos to bars.", "Use options to control conversion mode."}
                .append(help.parameterListHeading()) //e.g. %nPositional parameters:%n%n
                .append(help.parameterList())        //e.g. [FILE...] the files to convert
                .append(help.optionListHeading())    //e.g. %nOptions:%n%n
                .append(help.optionList())           //e.g. -h, --help   displays this help and exits
                .append(help.commandListHeading())   //e.g. %nCommands:%n%n
                .append(help.commandList())          //e.g.    add       adds the frup to the frooble
                .append(help.footerHeading())
                .append(help.footer());
        out.print(sb);
    }

    /**
     * Delegates to {@link #printVersionHelp(PrintStream, Help.Ansi)} with the {@linkplain Help.Ansi#AUTO platform default}.
     * @param out the printStream to print to
     * @see #printVersionHelp(PrintStream, Help.Ansi)
     * @since 0.9.8
     */
    public void printVersionHelp(final PrintStream out) { printVersionHelp(out, Help.Ansi.AUTO); }

    /**
     * Prints version information from the {@link Command#version()} annotation to the specified {@code PrintStream}.
     * Each element of the array of version strings is printed on a separate line. Version strings may contain
     * <a href="http://picocli.info/#_usage_help_with_styles_and_colors">markup for colors and style</a>.
     * @param out the printStream to print to
     * @param ansi whether the usage message should include ANSI escape codes or not
     * @see Command#version()
     * @see Option#versionHelp()
     * @see #isVersionHelpRequested()
     * @since 0.9.8
     */
    public void printVersionHelp(final PrintStream out, final Help.Ansi ansi) {
        for (final String versionInfo : versionLines) {
            out.println(ansi.new Text(versionInfo));
        }
    }
    /**
     * Prints version information from the {@link Command#version()} annotation to the specified {@code PrintStream}.
     * Each element of the array of version strings is {@linkplain String#format(String, Object...) formatted} with the
     * specified parameters, and printed on a separate line. Both version strings and parameters may contain
     * <a href="http://picocli.info/#_usage_help_with_styles_and_colors">markup for colors and style</a>.
     * @param out the printStream to print to
     * @param ansi whether the usage message should include ANSI escape codes or not
     * @param params Arguments referenced by the format specifiers in the version strings
     * @see Command#version()
     * @see Option#versionHelp()
     * @see #isVersionHelpRequested()
     * @since 1.0.0
     */
    public void printVersionHelp(final PrintStream out, final Help.Ansi ansi, final Object... params) {
        for (final String versionInfo : versionLines) {
            out.println(ansi.new Text(String.format(versionInfo, params)));
        }
    }

    /**
     * Delegates to {@link #call(Callable, PrintStream, Help.Ansi, String...)} with {@link Help.Ansi#AUTO}.
     * <p>
     * From picocli v2.0, this method prints usage help or version help if {@linkplain #printHelpIfRequested(List, PrintStream, Help.Ansi) requested},
     * and any exceptions thrown by the {@code Callable} are caught and rethrown wrapped in an {@code ExecutionException}.
     * </p>
     * @param callable the command to call when {@linkplain #parse(String...) parsing} succeeds.
     * @param out the printStream to print to
     * @param args the command line arguments to parse
     * @param <C> the annotated object must implement Callable
     * @param <T> the return type of the most specific command (must implement {@code Callable})
     * @see #call(Callable, PrintStream, Help.Ansi, String...)
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     * @throws ExecutionException if the Callable throws an exception
     * @return {@code null} if an error occurred while parsing the command line options, otherwise returns the result of calling the Callable
     * @see #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...)
     * @see RunFirst
     */
    public static <C extends Callable<T>, T> T call(final C callable, final PrintStream out, final String... args) {
        return call(callable, out, Help.Ansi.AUTO, args);
    }
    /**
     * Convenience method to allow command line application authors to avoid some boilerplate code in their application.
     * The annotated object needs to implement {@link Callable}. Calling this method is equivalent to:
     * <pre>
     * CommandLine cmd = new CommandLine(callable);
     * List&lt;CommandLine&gt; parsedCommands;
     * try {
     *     parsedCommands = cmd.parse(args);
     * } catch (ParameterException ex) {
     *     out.println(ex.getMessage());
     *     cmd.usage(out, ansi);
     *     return null;
     * }
     * if (CommandLine.printHelpIfRequested(parsedCommands, out, ansi)) {
     *     return null;
     * }
     * CommandLine last = parsedCommands.get(parsedCommands.size() - 1);
     * try {
     *     Callable&lt;Object&gt; subcommand = last.getCommand();
     *     return subcommand.call();
     * } catch (Exception ex) {
     *     throw new ExecutionException(last, "Error calling " + last.getCommand(), ex);
     * }
     * </pre>
     * <p>
     * If the specified Callable command has subcommands, the {@linkplain RunLast last} subcommand specified on the
     * command line is executed.
     * Commands with subcommands may be interested in calling the {@link #parseWithHandler(IParseResultHandler, PrintStream, String...) parseWithHandler}
     * method with a {@link RunAll} handler or a custom handler.
     * </p><p>
     * From picocli v2.0, this method prints usage help or version help if {@linkplain #printHelpIfRequested(List, PrintStream, Help.Ansi) requested},
     * and any exceptions thrown by the {@code Callable} are caught and rethrown wrapped in an {@code ExecutionException}.
     * </p>
     * @param callable the command to call when {@linkplain #parse(String...) parsing} succeeds.
     * @param out the printStream to print to
     * @param ansi whether the usage message should include ANSI escape codes or not
     * @param args the command line arguments to parse
     * @param <C> the annotated object must implement Callable
     * @param <T> the return type of the specified {@code Callable}
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     * @throws ExecutionException if the Callable throws an exception
     * @return {@code null} if an error occurred while parsing the command line options, or if help was requested and printed. Otherwise returns the result of calling the Callable
     * @see #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...)
     * @see RunLast
     */
    public static <C extends Callable<T>, T> T call(final C callable, final PrintStream out, final Help.Ansi ansi, final String... args) {
        final CommandLine cmd = new CommandLine(callable); // validate command outside of try-catch
        final List<Object> results = cmd.parseWithHandlers(new RunLast(), out, ansi, new DefaultExceptionHandler(), args);
        return results == null || results.isEmpty() ? null : (T) results.get(0);
    }

    /**
     * Delegates to {@link #run(Runnable, PrintStream, Help.Ansi, String...)} with {@link Help.Ansi#AUTO}.
     * <p>
     * From picocli v2.0, this method prints usage help or version help if {@linkplain #printHelpIfRequested(List, PrintStream, Help.Ansi) requested},
     * and any exceptions thrown by the {@code Runnable} are caught and rethrown wrapped in an {@code ExecutionException}.
     * </p>
     * @param runnable the command to run when {@linkplain #parse(String...) parsing} succeeds.
     * @param out the printStream to print to
     * @param args the command line arguments to parse
     * @param <R> the annotated object must implement Runnable
     * @see #run(Runnable, PrintStream, Help.Ansi, String...)
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     * @throws ExecutionException if the Runnable throws an exception
     * @see #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...)
     * @see RunFirst
     */
    public static <R extends Runnable> void run(final R runnable, final PrintStream out, final String... args) {
        run(runnable, out, Help.Ansi.AUTO, args);
    }
    /**
     * Convenience method to allow command line application authors to avoid some boilerplate code in their application.
     * The annotated object needs to implement {@link Runnable}. Calling this method is equivalent to:
     * <pre>
     * CommandLine cmd = new CommandLine(runnable);
     * List&lt;CommandLine&gt; parsedCommands;
     * try {
     *     parsedCommands = cmd.parse(args);
     * } catch (ParameterException ex) {
     *     out.println(ex.getMessage());
     *     cmd.usage(out, ansi);
     *     return null;
     * }
     * if (CommandLine.printHelpIfRequested(parsedCommands, out, ansi)) {
     *     return null;
     * }
     * CommandLine last = parsedCommands.get(parsedCommands.size() - 1);
     * try {
     *     Runnable subcommand = last.getCommand();
     *     subcommand.run();
     * } catch (Exception ex) {
     *     throw new ExecutionException(last, "Error running " + last.getCommand(), ex);
     * }
     * </pre>
     * <p>
     * If the specified Runnable command has subcommands, the {@linkplain RunLast last} subcommand specified on the
     * command line is executed.
     * Commands with subcommands may be interested in calling the {@link #parseWithHandler(IParseResultHandler, PrintStream, String...) parseWithHandler}
     * method with a {@link RunAll} handler or a custom handler.
     * </p><p>
     * From picocli v2.0, this method prints usage help or version help if {@linkplain #printHelpIfRequested(List, PrintStream, Help.Ansi) requested},
     * and any exceptions thrown by the {@code Runnable} are caught and rethrown wrapped in an {@code ExecutionException}.
     * </p>
     * @param runnable the command to run when {@linkplain #parse(String...) parsing} succeeds.
     * @param out the printStream to print to
     * @param ansi whether the usage message should include ANSI escape codes or not
     * @param args the command line arguments to parse
     * @param <R> the annotated object must implement Runnable
     * @throws InitializationException if the specified command object does not have a {@link Command}, {@link Option} or {@link Parameters} annotation
     * @throws ExecutionException if the Runnable throws an exception
     * @see #parseWithHandlers(IParseResultHandler, PrintStream, Help.Ansi, IExceptionHandler, String...)
     * @see RunLast
     */
    public static <R extends Runnable> void run(final R runnable, final PrintStream out, final Help.Ansi ansi, final String... args) {
        final CommandLine cmd = new CommandLine(runnable); // validate command outside of try-catch
        cmd.parseWithHandlers(new RunLast(), out, ansi, new DefaultExceptionHandler(), args);
    }

    /**
     * Registers the specified type converter for the specified class. When initializing fields annotated with
     * {@link Option}, the field's type is used as a lookup key to find the associated type converter, and this
     * type converter converts the original command line argument string value to the correct type.
     * <p>
     * Java 8 lambdas make it easy to register custom type converters:
     * </p>
     * <pre>
     * commandLine.registerConverter(java.nio.file.Path.class, s -&gt; java.nio.file.Paths.get(s));
     * commandLine.registerConverter(java.time.Duration.class, s -&gt; java.time.Duration.parse(s));</pre>
     * <p>
     * Built-in type converters are pre-registered for the following java 1.5 types:
     * </p>
     * <ul>
     *   <li>all primitive types</li>
     *   <li>all primitive wrapper types: Boolean, Byte, Character, Double, Float, Integer, Long, Short</li>
     *   <li>any enum</li>
     *   <li>java.io.File</li>
     *   <li>java.math.BigDecimal</li>
     *   <li>java.math.BigInteger</li>
     *   <li>java.net.InetAddress</li>
     *   <li>java.net.URI</li>
     *   <li>java.net.URL</li>
     *   <li>java.nio.charset.Charset</li>
     *   <li>java.sql.Time</li>
     *   <li>java.util.Date</li>
     *   <li>java.util.UUID</li>
     *   <li>java.util.regex.Pattern</li>
     *   <li>StringBuilder</li>
     *   <li>CharSequence</li>
     *   <li>String</li>
     * </ul>
     * <p>The specified converter will be registered with this {@code CommandLine} and the full hierarchy of its
     * subcommands and nested sub-subcommands <em>at the moment the converter is registered</em>. Subcommands added
     * later will not have this converter added automatically. To ensure a custom type converter is available to all
     * subcommands, register the type converter last, after adding subcommands.</p>
     *
     * @param cls the target class to convert parameter string values to
     * @param converter the class capable of converting string values to the specified target type
     * @param <K> the target type
     * @return this CommandLine object, to allow method chaining
     * @see #addSubcommand(String, Object)
     */
    public <K> CommandLine registerConverter(final Class<K> cls, final ITypeConverter<K> converter) {
        interpreter.converterRegistry.put(Assert.notNull(cls, "class"), Assert.notNull(converter, "converter"));
        for (final CommandLine command : interpreter.commands.values()) {
            command.registerConverter(cls, converter);
        }
        return this;
    }

    /** Returns the String that separates option names from option values when parsing command line options. {@value Help#DEFAULT_SEPARATOR} by default.
     * @return the String the parser uses to separate option names from option values */
    public String getSeparator() {
        return interpreter.separator;
    }

    /** Sets the String the parser uses to separate option names from option values to the specified value.
     * The separator may also be set declaratively with the {@link CommandLine.Command#separator()} annotation attribute.
     * @param separator the String that separates option names from option values
     * @return this {@code CommandLine} object, to allow method chaining */
    public CommandLine setSeparator(final String separator) {
        interpreter.separator = Assert.notNull(separator, "separator");
        return this;
    }

    /** Returns the command name (also called program name) displayed in the usage help synopsis. {@value Help#DEFAULT_COMMAND_NAME} by default.
     * @return the command name (also called program name) displayed in the usage */
    public String getCommandName() {
        return commandName;
    }

    /** Sets the command name (also called program name) displayed in the usage help synopsis to the specified value.
     * Note that this method only modifies the usage help message, it does not impact parsing behaviour.
     * The command name may also be set declaratively with the {@link CommandLine.Command#name()} annotation attribute.
     * @param commandName command name (also called program name) displayed in the usage help synopsis
     * @return this {@code CommandLine} object, to allow method chaining */
    public CommandLine setCommandName(final String commandName) {
        this.commandName = Assert.notNull(commandName, "commandName");
        return this;
    }
    private static boolean empty(final String str) { return str == null || str.trim().length() == 0; }
    private static boolean empty(final Object[] array) { return array == null || array.length == 0; }
    private static boolean empty(final Text txt) { return txt == null || txt.plain.toString().trim().length() == 0; }
    private static String str(final String[] arr, final int i) { return (arr == null || arr.length == 0) ? "" : arr[i]; }
    private static boolean isBoolean(final Class<?> type) { return type == Boolean.class || type == Boolean.TYPE; }
    private static CommandLine toCommandLine(final Object obj) { return obj instanceof CommandLine ? (CommandLine) obj : new CommandLine(obj);}
    private static boolean isMultiValue(final Field field) {  return isMultiValue(field.getType()); }
    private static boolean isMultiValue(final Class<?> cls) { return cls.isArray() || Collection.class.isAssignableFrom(cls) || Map.class.isAssignableFrom(cls); }
    private static Class<?>[] getTypeAttribute(final Field field) {
        final Class<?>[] explicit = field.isAnnotationPresent(Parameters.class) ? field.getAnnotation(Parameters.class).type() : field.getAnnotation(Option.class).type();
        if (explicit.length > 0) { return explicit; }
        if (field.getType().isArray()) { return new Class<?>[] { field.getType().getComponentType() }; }
        if (isMultiValue(field)) {
            final Type type = field.getGenericType(); // e.g. Map<Long, ? extends Number>
            if (type instanceof ParameterizedType) {
                final ParameterizedType parameterizedType = (ParameterizedType) type;
                final Type[] paramTypes = parameterizedType.getActualTypeArguments(); // e.g. ? extends Number
                final Class<?>[] result = new Class<?>[paramTypes.length];
                for (int i = 0; i < paramTypes.length; i++) {
                    if (paramTypes[i] instanceof Class) { result[i] = (Class<?>) paramTypes[i]; continue; } // e.g. Long
                    if (paramTypes[i] instanceof WildcardType) { // e.g. ? extends Number
                        final WildcardType wildcardType = (WildcardType) paramTypes[i];
                        final Type[] lower = wildcardType.getLowerBounds(); // e.g. []
                        if (lower.length > 0 && lower[0] instanceof Class) { result[i] = (Class<?>) lower[0]; continue; }
                        final Type[] upper = wildcardType.getUpperBounds(); // e.g. Number
                        if (upper.length > 0 && upper[0] instanceof Class) { result[i] = (Class<?>) upper[0]; continue; }
                    }
                    Arrays.fill(result, String.class); return result; // too convoluted generic type, giving up
                }
                return result; // we inferred all types from ParameterizedType
            }
            return new Class<?>[] {String.class, String.class}; // field is multi-value but not ParameterizedType
        }
        return new Class<?>[] {field.getType()}; // not a multi-value field
    }
    /**
     * <p>
     * Annotate fields in your class with {@code @Option} and picocli will initialize these fields when matching
     * arguments are specified on the command line.
     * </p><p>
     * For example:
     * </p>
     * <pre>import static picocli.CommandLine.*;
     *
     * public class MyClass {
     *     &#064;Parameters(type = File.class, description = "Any number of input files")
     *     private List&lt;File&gt; files = new ArrayList&lt;File&gt;();
     *
     *     &#064;Option(names = { "-o", "--out" }, description = "Output file (default: print to console)")
     *     private File outputFile;
     *
     *     &#064;Option(names = { "-v", "--verbose"}, description = "Verbosely list files processed")
     *     private boolean verbose;
     *
     *     &#064;Option(names = { "-h", "--help", "-?", "-help"}, usageHelp = true, description = "Display this help and exit")
     *     private boolean help;
     *
     *     &#064;Option(names = { "-V", "--version"}, versionHelp = true, description = "Display version information and exit")
     *     private boolean version;
     * }
     * </pre>
     * <p>
     * A field cannot be annotated with both {@code @Parameters} and {@code @Option} or a
     * {@code ParameterException} is thrown.
     * </p>
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    public @interface Option {
        /**
         * One or more option names. At least one option name is required.
         * <p>
         * Different environments have different conventions for naming options, but usually options have a prefix
         * that sets them apart from parameters.
         * Picocli supports all of the below styles. The default separator is {@code '='}, but this can be configured.
         * </p><p>
         * <b>*nix</b>
         * </p><p>
         * In Unix and Linux, options have a short (single-character) name, a long name or both.
         * Short options
         * (<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02">POSIX
         * style</a> are single-character and are preceded by the {@code '-'} character, e.g., {@code `-v'}.
         * <a href="https://www.gnu.org/software/tar/manual/html_node/Long-Options.html">GNU-style</a> long
         * (or <em>mnemonic</em>) options start with two dashes in a row, e.g., {@code `--file'}.
         * </p><p>Picocli supports the POSIX convention that short options can be grouped, with the last option
         * optionally taking a parameter, which may be attached to the option name or separated by a space or
         * a {@code '='} character. The below examples are all equivalent:
         * </p><pre>
         * -xvfFILE
         * -xvf FILE
         * -xvf=FILE
         * -xv --file FILE
         * -xv --file=FILE
         * -x -v --file FILE
         * -x -v --file=FILE
         * </pre><p>
         * <b>DOS</b>
         * </p><p>
         * DOS options mostly have upper case single-character names and start with a single slash {@code '/'} character.
         * Option parameters are separated by a {@code ':'} character. Options cannot be grouped together but
         * must be specified separately. For example:
         * </p><pre>
         * DIR /S /A:D /T:C
         * </pre><p>
         * <b>PowerShell</b>
         * </p><p>
         * Windows PowerShell options generally are a word preceded by a single {@code '-'} character, e.g., {@code `-Help'}.
         * Option parameters are separated by a space or by a {@code ':'} character.
         * </p>
         * @return one or more option names
         */
        String[] names();

        /**
         * Indicates whether this option is required. By default this is false.
         * If an option is required, but a user invokes the program without specifying the required option,
         * a {@link MissingParameterException} is thrown from the {@link #parse(String...)} method.
         * @return whether this option is required
         */
        boolean required() default false;

        /**
         * Set {@code help=true} if this option should disable validation of the remaining arguments:
         * If the {@code help} option is specified, no error message is generated for missing required options.
         * <p>
         * This attribute is useful for special options like help ({@code -h} and {@code --help} on unix,
         * {@code -?} and {@code -Help} on Windows) or version ({@code -V} and {@code --version} on unix,
         * {@code -Version} on Windows).
         * </p>
         * <p>
         * Note that the {@link #parse(String...)} method will not print help documentation. It will only set
         * the value of the annotated field. It is the responsibility of the caller to inspect the annotated fields
         * and take the appropriate action.
         * </p>
         * @return whether this option disables validation of the other arguments
         * @deprecated Use {@link #usageHelp()} and {@link #versionHelp()} instead. See {@link #printHelpIfRequested(List, PrintStream, CommandLine.Help.Ansi)}
         */
        boolean help() default false;

        /**
         * Set {@code usageHelp=true} if this option allows the user to request usage help. If this option is
         * specified on the command line, picocli will not validate the remaining arguments (so no "missing required
         * option" errors) and the {@link CommandLine#isUsageHelpRequested()} method will return {@code true}.
         * <p>
         * This attribute is useful for special options like help ({@code -h} and {@code --help} on unix,
         * {@code -?} and {@code -Help} on Windows).
         * </p>
         * <p>
         * Note that the {@link #parse(String...)} method will not print usage help documentation. It will only set
         * the value of the annotated field. It is the responsibility of the caller to inspect the annotated fields
         * and take the appropriate action.
         * </p>
         * @return whether this option allows the user to request usage help
         * @since 0.9.8
         */
        boolean usageHelp() default false;

        /**
         * Set {@code versionHelp=true} if this option allows the user to request version information. If this option is
         * specified on the command line, picocli will not validate the remaining arguments (so no "missing required
         * option" errors) and the {@link CommandLine#isVersionHelpRequested()} method will return {@code true}.
         * <p>
         * This attribute is useful for special options like version ({@code -V} and {@code --version} on unix,
         * {@code -Version} on Windows).
         * </p>
         * <p>
         * Note that the {@link #parse(String...)} method will not print version information. It will only set
         * the value of the annotated field. It is the responsibility of the caller to inspect the annotated fields
         * and take the appropriate action.
         * </p>
         * @return whether this option allows the user to request version information
         * @since 0.9.8
         */
        boolean versionHelp() default false;

        /**
         * Description of this option, used when generating the usage documentation.
         * @return the description of this option
         */
        String[] description() default {};

        /**
         * Specifies the minimum number of required parameters and the maximum number of accepted parameters.
         * If an option declares a positive arity, and the user specifies an insufficient number of parameters on the
         * command line, a {@link MissingParameterException} is thrown by the {@link #parse(String...)} method.
         * <p>
         * In many cases picocli can deduce the number of required parameters from the field's type.
         * By default, flags (boolean options) have arity zero,
         * and single-valued type fields (String, int, Integer, double, Double, File, Date, etc) have arity one.
         * Generally, fields with types that cannot hold multiple values can omit the {@code arity} attribute.
         * </p><p>
         * Fields used to capture options with arity two or higher should have a type that can hold multiple values,
         * like arrays or Collections. See {@link #type()} for strongly-typed Collection fields.
         * </p><p>
         * For example, if an option has 2 required parameters and any number of optional parameters,
         * specify {@code @Option(names = "-example", arity = "2..*")}.
         * </p>
         * <b>A note on boolean options</b>
         * <p>
         * By default picocli does not expect boolean options (also called "flags" or "switches") to have a parameter.
         * You can make a boolean option take a required parameter by annotating your field with {@code arity="1"}.
         * For example: </p>
         * <pre>&#064;Option(names = "-v", arity = "1") boolean verbose;</pre>
         * <p>
         * Because this boolean field is defined with arity 1, the user must specify either {@code <program> -v false}
         * or {@code <program> -v true}
         * on the command line, or a {@link MissingParameterException} is thrown by the {@link #parse(String...)}
         * method.
         * </p><p>
         * To make the boolean parameter possible but optional, define the field with {@code arity = "0..1"}.
         * For example: </p>
         * <pre>&#064;Option(names="-v", arity="0..1") boolean verbose;</pre>
         * <p>This will accept any of the below without throwing an exception:</p>
         * <pre>
         * -v
         * -v true
         * -v false
         * </pre>
         * @return how many arguments this option requires
         */
        String arity() default "";

        /**
         * Specify a {@code paramLabel} for the option parameter to be used in the usage help message. If omitted,
         * picocli uses the field name in fish brackets ({@code '<'} and {@code '>'}) by default. Example:
         * <pre>class Example {
         *     &#064;Option(names = {"-o", "--output"}, paramLabel="FILE", description="path of the output file")
         *     private File out;
         *     &#064;Option(names = {"-j", "--jobs"}, arity="0..1", description="Allow N jobs at once; infinite jobs with no arg.")
         *     private int maxJobs = -1;
         * }</pre>
         * <p>By default, the above gives a usage help message like the following:</p><pre>
         * Usage: &lt;main class&gt; [OPTIONS]
         * -o, --output FILE       path of the output file
         * -j, --jobs [&lt;maxJobs&gt;]  Allow N jobs at once; infinite jobs with no arg.
         * </pre>
         * @return name of the option parameter used in the usage help message
         */
        String paramLabel() default "";

        /** <p>
         * Optionally specify a {@code type} to control exactly what Class the option parameter should be converted
         * to. This may be useful when the field type is an interface or an abstract class. For example, a field can
         * be declared to have type {@code java.lang.Number}, and annotating {@code @Option(type=Short.class)}
         * ensures that the option parameter value is converted to a {@code Short} before setting the field value.
         * </p><p>
         * For array fields whose <em>component</em> type is an interface or abstract class, specify the concrete <em>component</em> type.
         * For example, a field with type {@code Number[]} may be annotated with {@code @Option(type=Short.class)}
         * to ensure that option parameter values are converted to {@code Short} before adding an element to the array.
         * </p><p>
         * Picocli will use the {@link ITypeConverter} that is
         * {@linkplain #registerConverter(Class, ITypeConverter) registered} for the specified type to convert
         * the raw String values before modifying the field value.
         * </p><p>
         * Prior to 2.0, the {@code type} attribute was necessary for {@code Collection} and {@code Map} fields,
         * but starting from 2.0 picocli will infer the component type from the generic type's type arguments.
         * For example, for a field of type {@code Map<TimeUnit, Long>} picocli will know the option parameter
         * should be split up in key=value pairs, where the key should be converted to a {@code java.util.concurrent.TimeUnit}
         * enum value, and the value should be converted to a {@code Long}. No {@code @Option(type=...)} type attribute
         * is required for this. For generic types with wildcards, picocli will take the specified upper or lower bound
         * as the Class to convert to, unless the {@code @Option} annotation specifies an explicit {@code type} attribute.
         * </p><p>
         * If the field type is a raw collection or a raw map, and you want it to contain other values than Strings,
         * or if the generic type's type arguments are interfaces or abstract classes, you may
         * specify a {@code type} attribute to control the Class that the option parameter should be converted to.
         * @return the type(s) to convert the raw String values
         */
        Class<?>[] type() default {};

        /**
         * Specify a regular expression to use to split option parameter values before applying them to the field.
         * All elements resulting from the split are added to the array or Collection. Ignored for single-value fields.
         * @return a regular expression to split option parameter values or {@code ""} if the value should not be split
         * @see String#split(String)
         */
        String split() default "";

        /**
         * Set {@code hidden=true} if this option should not be included in the usage documentation.
         * @return whether this option should be excluded from the usage message
         */
        boolean hidden() default false;
    }
    /**
     * <p>
     * Fields annotated with {@code @Parameters} will be initialized with positional parameters. By specifying the
     * {@link #index()} attribute you can pick which (or what range) of the positional parameters to apply. If no index
     * is specified, the field will get all positional parameters (so it should be an array or a collection).
     * </p><p>
     * When parsing the command line arguments, picocli first tries to match arguments to {@link Option Options}.
     * Positional parameters are the arguments that follow the options, or the arguments that follow a "--" (double
     * dash) argument on the command line.
     * </p><p>
     * For example:
     * </p>
     * <pre>import static picocli.CommandLine.*;
     *
     * public class MyCalcParameters {
     *     &#064;Parameters(type = BigDecimal.class, description = "Any number of input numbers")
     *     private List&lt;BigDecimal&gt; files = new ArrayList&lt;BigDecimal&gt;();
     *
     *     &#064;Option(names = { "-h", "--help", "-?", "-help"}, help = true, description = "Display this help and exit")
     *     private boolean help;
     * }
     * </pre><p>
     * A field cannot be annotated with both {@code @Parameters} and {@code @Option} or a {@code ParameterException}
     * is thrown.</p>
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    public @interface Parameters {
        /** Specify an index ("0", or "1", etc.) to pick which of the command line arguments should be assigned to this
         * field. For array or Collection fields, you can also specify an index range ("0..3", or "2..*", etc.) to assign
         * a subset of the command line arguments to this field. The default is "*", meaning all command line arguments.
         * @return an index or range specifying which of the command line arguments should be assigned to this field
         */
        String index() default "*";

        /** Description of the parameter(s), used when generating the usage documentation.
         * @return the description of the parameter(s)
         */
        String[] description() default {};

        /**
         * Specifies the minimum number of required parameters and the maximum number of accepted parameters. If a
         * positive arity is declared, and the user specifies an insufficient number of parameters on the command line,
         * {@link MissingParameterException} is thrown by the {@link #parse(String...)} method.
         * <p>The default depends on the type of the parameter: booleans require no parameters, arrays and Collections
         * accept zero to any number of parameters, and any other type accepts one parameter.</p>
         * @return the range of minimum and maximum parameters accepted by this command
         */
        String arity() default "";

        /**
         * Specify a {@code paramLabel} for the parameter to be used in the usage help message. If omitted,
         * picocli uses the field name in fish brackets ({@code '<'} and {@code '>'}) by default. Example:
         * <pre>class Example {
         *     &#064;Parameters(paramLabel="FILE", description="path of the input FILE(s)")
         *     private File[] inputFiles;
         * }</pre>
         * <p>By default, the above gives a usage help message like the following:</p><pre>
         * Usage: &lt;main class&gt; [FILE...]
         * [FILE...]       path of the input FILE(s)
         * </pre>
         * @return name of the positional parameter used in the usage help message
         */
        String paramLabel() default "";

        /**
         * <p>
         * Optionally specify a {@code type} to control exactly what Class the positional parameter should be converted
         * to. This may be useful when the field type is an interface or an abstract class. For example, a field can
         * be declared to have type {@code java.lang.Number}, and annotating {@code @Parameters(type=Short.class)}
         * ensures that the positional parameter value is converted to a {@code Short} before setting the field value.
         * </p><p>
         * For array fields whose <em>component</em> type is an interface or abstract class, specify the concrete <em>component</em> type.
         * For example, a field with type {@code Number[]} may be annotated with {@code @Parameters(type=Short.class)}
         * to ensure that positional parameter values are converted to {@code Short} before adding an element to the array.
         * </p><p>
         * Picocli will use the {@link ITypeConverter} that is
         * {@linkplain #registerConverter(Class, ITypeConverter) registered} for the specified type to convert
         * the raw String values before modifying the field value.
         * </p><p>
         * Prior to 2.0, the {@code type} attribute was necessary for {@code Collection} and {@code Map} fields,
         * but starting from 2.0 picocli will infer the component type from the generic type's type arguments.
         * For example, for a field of type {@code Map<TimeUnit, Long>} picocli will know the positional parameter
         * should be split up in key=value pairs, where the key should be converted to a {@code java.util.concurrent.TimeUnit}
         * enum value, and the value should be converted to a {@code Long}. No {@code @Parameters(type=...)} type attribute
         * is required for this. For generic types with wildcards, picocli will take the specified upper or lower bound
         * as the Class to convert to, unless the {@code @Parameters} annotation specifies an explicit {@code type} attribute.
         * </p><p>
         * If the field type is a raw collection or a raw map, and you want it to contain other values than Strings,
         * or if the generic type's type arguments are interfaces or abstract classes, you may
         * specify a {@code type} attribute to control the Class that the positional parameter should be converted to.
         * @return the type(s) to convert the raw String values
         */
        Class<?>[] type() default {};

        /**
         * Specify a regular expression to use to split positional parameter values before applying them to the field.
         * All elements resulting from the split are added to the array or Collection. Ignored for single-value fields.
         * @return a regular expression to split operand values or {@code ""} if the value should not be split
         * @see String#split(String)
         */
        String split() default "";

        /**
         * Set {@code hidden=true} if this parameter should not be included in the usage message.
         * @return whether this parameter should be excluded from the usage message
         */
        boolean hidden() default false;
    }

    /**
     * <p>Annotate your class with {@code @Command} when you want more control over the format of the generated help
     * message.
     * </p><pre>
     * &#064;Command(name      = "Encrypt",
     *        description = "Encrypt FILE(s), or standard input, to standard output or to the output file.",
     *        footer      = "Copyright (c) 2017")
     * public class Encrypt {
     *     &#064;Parameters(paramLabel = "FILE", type = File.class, description = "Any number of input files")
     *     private List&lt;File&gt; files     = new ArrayList&lt;File&gt;();
     *
     *     &#064;Option(names = { "-o", "--out" }, description = "Output file (default: print to console)")
     *     private File outputFile;
     * }</pre>
     * <p>
     * The structure of a help message looks like this:
     * </p><ul>
     *   <li>[header]</li>
     *   <li>[synopsis]: {@code Usage: <commandName> [OPTIONS] [FILE...]}</li>
     *   <li>[description]</li>
     *   <li>[parameter list]: {@code      [FILE...]   Any number of input files}</li>
     *   <li>[option list]: {@code   -h, --help   prints this help message and exits}</li>
     *   <li>[footer]</li>
     * </ul> */
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.TYPE, ElementType.LOCAL_VARIABLE, ElementType.PACKAGE})
    public @interface Command {
        /** Program name to show in the synopsis. If omitted, {@code "<main class>"} is used.
         * For {@linkplain #subcommands() declaratively added} subcommands, this attribute is also used
         * by the parser to recognize subcommands in the command line arguments.
         * @return the program name to show in the synopsis
         * @see Help#commandName */
        String name() default "<main class>";

        /** A list of classes to instantiate and register as subcommands. When registering subcommands declaratively
         * like this, you don't need to call the {@link CommandLine#addSubcommand(String, Object)} method. For example, this:
         * <pre>
         * &#064;Command(subcommands = {
         *         GitStatus.class,
         *         GitCommit.class,
         *         GitBranch.class })
         * public class Git { ... }
         *
         * CommandLine commandLine = new CommandLine(new Git());
         * </pre> is equivalent to this:
         * <pre>
         * // alternative: programmatically add subcommands.
         * // NOTE: in this case there should be no `subcommands` attribute on the @Command annotation.
         * &#064;Command public class Git { ... }
         *
         * CommandLine commandLine = new CommandLine(new Git())
         *         .addSubcommand("status",   new GitStatus())
         *         .addSubcommand("commit",   new GitCommit())
         *         .addSubcommand("branch",   new GitBranch());
         * </pre>
         * @return the declaratively registered subcommands of this command, or an empty array if none
         * @see CommandLine#addSubcommand(String, Object)
         * @since 0.9.8
         */
        Class<?>[] subcommands() default {};

        /** String that separates options from option parameters. Default is {@code "="}. Spaces are also accepted.
         * @return the string that separates options from option parameters, used both when parsing and when generating usage help
         * @see Help#separator
         * @see CommandLine#setSeparator(String) */
        String separator() default "=";

        /** Version information for this command, to print to the console when the user specifies an
         * {@linkplain Option#versionHelp() option} to request version help. This is not part of the usage help message.
         *
         * @return a string or an array of strings with version information about this command.
         * @since 0.9.8
         * @see CommandLine#printVersionHelp(PrintStream)
         */
        String[] version() default {};

        /** Set the heading preceding the header section. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * @return the heading preceding the header section
         * @see Help#headerHeading(Object...)  */
        String headerHeading() default "";

        /** Optional summary description of the command, shown before the synopsis.
         * @return summary description of the command
         * @see Help#header
         * @see Help#header(Object...)  */
        String[] header() default {};

        /** Set the heading preceding the synopsis text. May contain embedded
         * {@linkplain java.util.Formatter format specifiers}. The default heading is {@code "Usage: "} (without a line
         * break between the heading and the synopsis text).
         * @return the heading preceding the synopsis text
         * @see Help#synopsisHeading(Object...)  */
        String synopsisHeading() default "Usage: ";

        /** Specify {@code true} to generate an abbreviated synopsis like {@code "<main> [OPTIONS] [PARAMETERS...]"}.
         * By default, a detailed synopsis with individual option names and parameters is generated.
         * @return whether the synopsis should be abbreviated
         * @see Help#abbreviateSynopsis
         * @see Help#abbreviatedSynopsis()
         * @see Help#detailedSynopsis(Comparator, boolean) */
        boolean abbreviateSynopsis() default false;

        /** Specify one or more custom synopsis lines to display instead of an auto-generated synopsis.
         * @return custom synopsis text to replace the auto-generated synopsis
         * @see Help#customSynopsis
         * @see Help#customSynopsis(Object...) */
        String[] customSynopsis() default {};

        /** Set the heading preceding the description section. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * @return the heading preceding the description section
         * @see Help#descriptionHeading(Object...)  */
        String descriptionHeading() default "";

        /** Optional text to display between the synopsis line(s) and the list of options.
         * @return description of this command
         * @see Help#description
         * @see Help#description(Object...) */
        String[] description() default {};

        /** Set the heading preceding the parameters list. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * @return the heading preceding the parameters list
         * @see Help#parameterListHeading(Object...)  */
        String parameterListHeading() default "";

        /** Set the heading preceding the options list. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * @return the heading preceding the options list
         * @see Help#optionListHeading(Object...)  */
        String optionListHeading() default "";

        /** Specify {@code false} to show Options in declaration order. The default is to sort alphabetically.
         * @return whether options should be shown in alphabetic order.
         * @see Help#sortOptions */
        boolean sortOptions() default true;

        /** Prefix required options with this character in the options list. The default is no marker: the synopsis
         * indicates which options and parameters are required.
         * @return the character to show in the options list to mark required options
         * @see Help#requiredOptionMarker */
        char requiredOptionMarker() default ' ';

        /** Specify {@code true} to show default values in the description column of the options list (except for
         * boolean options). False by default.
         * @return whether the default values for options and parameters should be shown in the description column
         * @see Help#showDefaultValues */
        boolean showDefaultValues() default false;

        /** Set the heading preceding the subcommands list. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * The default heading is {@code "Commands:%n"} (with a line break at the end).
         * @return the heading preceding the subcommands list
         * @see Help#commandListHeading(Object...)  */
        String commandListHeading() default "Commands:%n";

        /** Set the heading preceding the footer section. May contain embedded {@linkplain java.util.Formatter format specifiers}.
         * @return the heading preceding the footer section
         * @see Help#footerHeading(Object...)  */
        String footerHeading() default "";

        /** Optional text to display after the list of options.
         * @return text to display after the list of options
         * @see Help#footer
         * @see Help#footer(Object...) */
        String[] footer() default {};
    }
    /**
     * <p>
     * When parsing command line arguments and initializing
     * fields annotated with {@link Option @Option} or {@link Parameters @Parameters},
     * String values can be converted to any type for which a {@code ITypeConverter} is registered.
     * </p><p>
     * This interface defines the contract for classes that know how to convert a String into some domain object.
     * Custom converters can be registered with the {@link #registerConverter(Class, ITypeConverter)} method.
     * </p><p>
     * Java 8 lambdas make it easy to register custom type converters:
     * </p>
     * <pre>
     * commandLine.registerConverter(java.nio.file.Path.class, s -&gt; java.nio.file.Paths.get(s));
     * commandLine.registerConverter(java.time.Duration.class, s -&gt; java.time.Duration.parse(s));</pre>
     * <p>
     * Built-in type converters are pre-registered for the following java 1.5 types:
     * </p>
     * <ul>
     *   <li>all primitive types</li>
     *   <li>all primitive wrapper types: Boolean, Byte, Character, Double, Float, Integer, Long, Short</li>
     *   <li>any enum</li>
     *   <li>java.io.File</li>
     *   <li>java.math.BigDecimal</li>
     *   <li>java.math.BigInteger</li>
     *   <li>java.net.InetAddress</li>
     *   <li>java.net.URI</li>
     *   <li>java.net.URL</li>
     *   <li>java.nio.charset.Charset</li>
     *   <li>java.sql.Time</li>
     *   <li>java.util.Date</li>
     *   <li>java.util.UUID</li>
     *   <li>java.util.regex.Pattern</li>
     *   <li>StringBuilder</li>
     *   <li>CharSequence</li>
     *   <li>String</li>
     * </ul>
     * @param <K> the type of the object that is the result of the conversion
     */
    public interface ITypeConverter<K> {
        /**
         * Converts the specified command line argument value to some domain object.
         * @param value the command line argument String value
         * @return the resulting domain object
         * @throws Exception an exception detailing what went wrong during the conversion
         */
        K convert(String value) throws Exception;
    }
    /** Describes the number of parameters required and accepted by an option or a positional parameter.
     * @since 0.9.7
     */
    public static class Range implements Comparable<Range> {
        /** Required number of parameters for an option or positional parameter. */
        public final int min;
        /** Maximum accepted number of parameters for an option or positional parameter. */
        public final int max;
        public final boolean isVariable;
        private final boolean isUnspecified;
        private final String originalValue;

        /** Constructs a new Range object with the specified parameters.
         * @param min minimum number of required parameters
         * @param max maximum number of allowed parameters (or Integer.MAX_VALUE if variable)
         * @param variable {@code true} if any number or parameters is allowed, {@code false} otherwise
         * @param unspecified {@code true} if no arity was specified on the option/parameter (value is based on type)
         * @param originalValue the original value that was specified on the option or parameter
         */
        public Range(final int min, final int max, final boolean variable, final boolean unspecified, final String originalValue) {
            this.min = min;
            this.max = max;
            this.isVariable = variable;
            this.isUnspecified = unspecified;
            this.originalValue = originalValue;
        }
        /** Returns a new {@code Range} based on the {@link Option#arity()} annotation on the specified field,
         * or the field type's default arity if no arity was specified.
         * @param field the field whose Option annotation to inspect
         * @return a new {@code Range} based on the Option arity annotation on the specified field */
        public static Range optionArity(final Field field) {
            return field.isAnnotationPresent(Option.class)
                    ? adjustForType(Range.valueOf(field.getAnnotation(Option.class).arity()), field)
                    : new Range(0, 0, false, true, "0");
        }
        /** Returns a new {@code Range} based on the {@link Parameters#arity()} annotation on the specified field,
         * or the field type's default arity if no arity was specified.
         * @param field the field whose Parameters annotation to inspect
         * @return a new {@code Range} based on the Parameters arity annotation on the specified field */
        public static Range parameterArity(final Field field) {
            return field.isAnnotationPresent(Parameters.class)
                    ? adjustForType(Range.valueOf(field.getAnnotation(Parameters.class).arity()), field)
                    : new Range(0, 0, false, true, "0");
        }
        /** Returns a new {@code Range} based on the {@link Parameters#index()} annotation on the specified field.
         * @param field the field whose Parameters annotation to inspect
         * @return a new {@code Range} based on the Parameters index annotation on the specified field */
        public static Range parameterIndex(final Field field) {
            return field.isAnnotationPresent(Parameters.class)
                    ? Range.valueOf(field.getAnnotation(Parameters.class).index())
                    : new Range(0, 0, false, true, "0");
        }
        static Range adjustForType(final Range result, final Field field) {
            return result.isUnspecified ? defaultArity(field) : result;
        }
        /** Returns the default arity {@code Range}: for {@link Option options} this is 0 for booleans and 1 for
         * other types, for {@link Parameters parameters} booleans have arity 0, arrays or Collections have
         * arity "0..*", and other types have arity 1.
         * @param field the field whose default arity to return
         * @return a new {@code Range} indicating the default arity of the specified field
         * @since 2.0 */
        public static Range defaultArity(final Field field) {
            final Class<?> type = field.getType();
            if (field.isAnnotationPresent(Option.class)) {
                return defaultArity(type);
            }
            if (isMultiValue(type)) {
                return Range.valueOf("0..1");
            }
            return Range.valueOf("1");// for single-valued fields (incl. boolean positional parameters)
        }
        /** Returns the default arity {@code Range} for {@link Option options}: booleans have arity 0, other types have arity 1.
         * @param type the type whose default arity to return
         * @return a new {@code Range} indicating the default arity of the specified type */
        public static Range defaultArity(final Class<?> type) {
            return isBoolean(type) ? Range.valueOf("0") : Range.valueOf("1");
        }
        private int size() { return 1 + max - min; }
        static Range parameterCapacity(final Field field) {
            final Range arity = parameterArity(field);
            if (!isMultiValue(field)) { return arity; }
            final Range index = parameterIndex(field);
            if (arity.max == 0)    { return arity; }
            if (index.size() == 1) { return arity; }
            if (index.isVariable)  { return Range.valueOf(arity.min + "..*"); }
            if (arity.size() == 1) { return Range.valueOf(arity.min * index.size() + ""); }
            if (arity.isVariable)  { return Range.valueOf(arity.min * index.size() + "..*"); }
            return Range.valueOf(arity.min * index.size() + ".." + arity.max * index.size());
        }
        /** Leniently parses the specified String as an {@code Range} value and return the result. A range string can
         * be a fixed integer value or a range of the form {@code MIN_VALUE + ".." + MAX_VALUE}. If the
         * {@code MIN_VALUE} string is not numeric, the minimum is zero. If the {@code MAX_VALUE} is not numeric, the
         * range is taken to be variable and the maximum is {@code Integer.MAX_VALUE}.
         * @param range the value range string to parse
         * @return a new {@code Range} value */
        public static Range valueOf(String range) {
            range = range.trim();
            final boolean unspecified = range.length() == 0 || range.startsWith(".."); // || range.endsWith("..");
            int min = -1, max = -1;
            boolean variable = false;
            int dots = -1;
            if ((dots = range.indexOf("..")) >= 0) {
                min = parseInt(range.substring(0, dots), 0);
                max = parseInt(range.substring(dots + 2), Integer.MAX_VALUE);
                variable = max == Integer.MAX_VALUE;
            } else {
                max = parseInt(range, Integer.MAX_VALUE);
                variable = max == Integer.MAX_VALUE;
                min = variable ? 0 : max;
            }
            final Range result = new Range(min, max, variable, unspecified, range);
            return result;
        }
        private static int parseInt(final String str, final int defaultValue) {
            try {
                return Integer.parseInt(str);
            } catch (final Exception ex) {
                return defaultValue;
            }
        }
        /** Returns a new Range object with the {@code min} value replaced by the specified value.
         * The {@code max} of the returned Range is guaranteed not to be less than the new {@code min} value.
         * @param newMin the {@code min} value of the returned Range object
         * @return a new Range object with the specified {@code min} value */
        public Range min(final int newMin) { return new Range(newMin, Math.max(newMin, max), isVariable, isUnspecified, originalValue); }

        /** Returns a new Range object with the {@code max} value replaced by the specified value.
         * The {@code min} of the returned Range is guaranteed not to be greater than the new {@code max} value.
         * @param newMax the {@code max} value of the returned Range object
         * @return a new Range object with the specified {@code max} value */
        public Range max(final int newMax) { return new Range(Math.min(min, newMax), newMax, isVariable, isUnspecified, originalValue); }

        /**
         * Returns {@code true} if this Range includes the specified value, {@code false} otherwise.
         * @param value the value to check
         * @return {@code true} if the specified value is not less than the minimum and not greater than the maximum of this Range
         */
        public boolean contains(final int value) { return min <= value && max >= value; }

        @Override
        public boolean equals(final Object object) {
            if (!(object instanceof Range)) { return false; }
            final Range other = (Range) object;
            return other.max == this.max && other.min == this.min && other.isVariable == this.isVariable;
        }
        @Override
        public int hashCode() {
            return ((17 * 37 + max) * 37 + min) * 37 + (isVariable ? 1 : 0);
        }
        @Override
        public String toString() {
            return min == max ? String.valueOf(min) : min + ".." + (isVariable ? "*" : max);
        }
        @Override
        public int compareTo(final Range other) {
            final int result = min - other.min;
            return (result == 0) ? max - other.max : result;
        }
    }
    static void init(final Class<?> cls,
                              final List<Field> requiredFields,
                              final Map<String, Field> optionName2Field,
                              final Map<Character, Field> singleCharOption2Field,
                              final List<Field> positionalParametersFields) {
        final Field[] declaredFields = cls.getDeclaredFields();
        for (final Field field : declaredFields) {
            field.setAccessible(true);
            if (field.isAnnotationPresent(Option.class)) {
                final Option option = field.getAnnotation(Option.class);
                if (option.required()) {
                    requiredFields.add(field);
                }
                for (final String name : option.names()) { // cannot be null or empty
                    final Field existing = optionName2Field.put(name, field);
                    if (existing != null && existing != field) {
                        throw DuplicateOptionAnnotationsException.create(name, field, existing);
                    }
                    if (name.length() == 2 && name.startsWith("-")) {
                        final char flag = name.charAt(1);
                        final Field existing2 = singleCharOption2Field.put(flag, field);
                        if (existing2 != null && existing2 != field) {
                            throw DuplicateOptionAnnotationsException.create(name, field, existing2);
                        }
                    }
                }
            }
            if (field.isAnnotationPresent(Parameters.class)) {
                if (field.isAnnotationPresent(Option.class)) {
                    throw new DuplicateOptionAnnotationsException("A field can be either @Option or @Parameters, but '"
                            + field.getName() + "' is both.");
                }
                positionalParametersFields.add(field);
                final Range arity = Range.parameterArity(field);
                if (arity.min > 0) {
                    requiredFields.add(field);
                }
            }
        }
    }
    static void validatePositionalParameters(final List<Field> positionalParametersFields) {
        int min = 0;
        for (final Field field : positionalParametersFields) {
            final Range index = Range.parameterIndex(field);
            if (index.min > min) {
                throw new ParameterIndexGapException("Missing field annotated with @Parameter(index=" + min +
                        "). Nearest field '" + field.getName() + "' has index=" + index.min);
            }
            min = Math.max(min, index.max);
            min = min == Integer.MAX_VALUE ? min : min + 1;
        }
    }
    private static <T> Stack<T> reverse(final Stack<T> stack) {
        Collections.reverse(stack);
        return stack;
    }
    /**
     * Helper class responsible for processing command line arguments.
     */
    private class Interpreter {
        private final Map<String, CommandLine> commands                  = new LinkedHashMap<>();
        private final Map<Class<?>, ITypeConverter<?>> converterRegistry = new HashMap<>();
        private final Map<String, Field> optionName2Field                = new HashMap<>();
        private final Map<Character, Field> singleCharOption2Field       = new HashMap<>();
        private final List<Field> requiredFields                         = new ArrayList<>();
        private final List<Field> positionalParametersFields             = new ArrayList<>();
        private final Object command;
        private boolean isHelpRequested;
        private String separator = Help.DEFAULT_SEPARATOR;
        private int position;

        Interpreter(final Object command) {
            converterRegistry.put(Path.class,          new BuiltIn.PathConverter());
            converterRegistry.put(Object.class,        new BuiltIn.StringConverter());
            converterRegistry.put(String.class,        new BuiltIn.StringConverter());
            converterRegistry.put(StringBuilder.class, new BuiltIn.StringBuilderConverter());
            converterRegistry.put(CharSequence.class,  new BuiltIn.CharSequenceConverter());
            converterRegistry.put(Byte.class,          new BuiltIn.ByteConverter());
            converterRegistry.put(Byte.TYPE,           new BuiltIn.ByteConverter());
            converterRegistry.put(Boolean.class,       new BuiltIn.BooleanConverter());
            converterRegistry.put(Boolean.TYPE,        new BuiltIn.BooleanConverter());
            converterRegistry.put(Character.class,     new BuiltIn.CharacterConverter());
            converterRegistry.put(Character.TYPE,      new BuiltIn.CharacterConverter());
            converterRegistry.put(Short.class,         new BuiltIn.ShortConverter());
            converterRegistry.put(Short.TYPE,          new BuiltIn.ShortConverter());
            converterRegistry.put(Integer.class,       new BuiltIn.IntegerConverter());
            converterRegistry.put(Integer.TYPE,        new BuiltIn.IntegerConverter());
            converterRegistry.put(Long.class,          new BuiltIn.LongConverter());
            converterRegistry.put(Long.TYPE,           new BuiltIn.LongConverter());
            converterRegistry.put(Float.class,         new BuiltIn.FloatConverter());
            converterRegistry.put(Float.TYPE,          new BuiltIn.FloatConverter());
            converterRegistry.put(Double.class,        new BuiltIn.DoubleConverter());
            converterRegistry.put(Double.TYPE,         new BuiltIn.DoubleConverter());
            converterRegistry.put(File.class,          new BuiltIn.FileConverter());
            converterRegistry.put(URI.class,           new BuiltIn.URIConverter());
            converterRegistry.put(URL.class,           new BuiltIn.URLConverter());
            converterRegistry.put(Date.class,          new BuiltIn.ISO8601DateConverter());
            converterRegistry.put(Time.class,          new BuiltIn.ISO8601TimeConverter());
            converterRegistry.put(BigDecimal.class,    new BuiltIn.BigDecimalConverter());
            converterRegistry.put(BigInteger.class,    new BuiltIn.BigIntegerConverter());
            converterRegistry.put(Charset.class,       new BuiltIn.CharsetConverter());
            converterRegistry.put(InetAddress.class,   new BuiltIn.InetAddressConverter());
            converterRegistry.put(Pattern.class,       new BuiltIn.PatternConverter());
            converterRegistry.put(UUID.class,          new BuiltIn.UUIDConverter());

            this.command                 = Assert.notNull(command, "command");
            Class<?> cls                 = command.getClass();
            String declaredName          = null;
            String declaredSeparator     = null;
            boolean hasCommandAnnotation = false;
            while (cls != null) {
                init(cls, requiredFields, optionName2Field, singleCharOption2Field, positionalParametersFields);
                if (cls.isAnnotationPresent(Command.class)) {
                    hasCommandAnnotation = true;
                    final Command cmd = cls.getAnnotation(Command.class);
                    declaredSeparator = (declaredSeparator == null) ? cmd.separator() : declaredSeparator;
                    declaredName = (declaredName == null) ? cmd.name() : declaredName;
                    CommandLine.this.versionLines.addAll(Arrays.asList(cmd.version()));

                    for (final Class<?> sub : cmd.subcommands()) {
                        final Command subCommand = sub.getAnnotation(Command.class);
                        if (subCommand == null || Help.DEFAULT_COMMAND_NAME.equals(subCommand.name())) {
                            throw new InitializationException("Subcommand " + sub.getName() +
                                    " is missing the mandatory @Command annotation with a 'name' attribute");
                        }
                        try {
                            final Constructor<?> constructor = sub.getDeclaredConstructor();
                            constructor.setAccessible(true);
                            final CommandLine commandLine = toCommandLine(constructor.newInstance());
                            commandLine.parent = CommandLine.this;
                            commands.put(subCommand.name(), commandLine);
                        }
                        catch (final InitializationException ex) { throw ex; }
                        catch (final NoSuchMethodException ex) { throw new InitializationException("Cannot instantiate subcommand " +
                                sub.getName() + ": the class has no constructor", ex); }
                        catch (final Exception ex) {
                            throw new InitializationException("Could not instantiate and add subcommand " +
                                    sub.getName() + ": " + ex, ex);
                        }
                    }
                }
                cls = cls.getSuperclass();
            }
            separator = declaredSeparator != null ? declaredSeparator : separator;
            CommandLine.this.commandName = declaredName != null ? declaredName : CommandLine.this.commandName;
            Collections.sort(positionalParametersFields, new PositionalParametersSorter());
            validatePositionalParameters(positionalParametersFields);

            if (positionalParametersFields.isEmpty() && optionName2Field.isEmpty() && !hasCommandAnnotation) {
                throw new InitializationException(command + " (" + command.getClass() +
                        ") is not a command: it has no @Command, @Option or @Parameters annotations");
            }
        }

        /**
         * Entry point into parsing command line arguments.
         * @param args the command line arguments
         * @return a list with all commands and subcommands initialized by this method
         * @throws ParameterException if the specified command line arguments are invalid
         */
        List<CommandLine> parse(final String... args) {
            Assert.notNull(args, "argument array");
            if (tracer.isInfo()) {tracer.info("Parsing %d command line args %s%n", args.length, Arrays.toString(args));}
            final Stack<String> arguments = new Stack<>();
            for (int i = args.length - 1; i >= 0; i--) {
                arguments.push(args[i]);
            }
            final List<CommandLine> result = new ArrayList<>();
            parse(result, arguments, args);
            return result;
        }

        private void parse(final List<CommandLine> parsedCommands, final Stack<String> argumentStack, final String[] originalArgs) {
            // first reset any state in case this CommandLine instance is being reused
            isHelpRequested = false;
            CommandLine.this.versionHelpRequested = false;
            CommandLine.this.usageHelpRequested = false;

            final Class<?> cmdClass = this.command.getClass();
            if (tracer.isDebug()) {tracer.debug("Initializing %s: %d options, %d positional parameters, %d required, %d subcommands.%n", cmdClass.getName(), new HashSet<>(optionName2Field.values()).size(), positionalParametersFields.size(), requiredFields.size(), commands.size());}
            parsedCommands.add(CommandLine.this);
            final List<Field> required = new ArrayList<>(requiredFields);
            final Set<Field> initialized = new HashSet<>();
            Collections.sort(required, new PositionalParametersSorter());
            try {
                processArguments(parsedCommands, argumentStack, required, initialized, originalArgs);
            } catch (final ParameterException ex) {
                throw ex;
            } catch (final Exception ex) {
                final int offendingArgIndex = originalArgs.length - argumentStack.size() - 1;
                final String arg = offendingArgIndex >= 0 && offendingArgIndex < originalArgs.length ? originalArgs[offendingArgIndex] : "?";
                throw ParameterException.create(CommandLine.this, ex, arg, offendingArgIndex, originalArgs);
            }
            if (!isAnyHelpRequested() && !required.isEmpty()) {
                for (final Field missing : required) {
                    if (missing.isAnnotationPresent(Option.class)) {
                        throw MissingParameterException.create(CommandLine.this, required, separator);
                    } else {
                        assertNoMissingParameters(missing, Range.parameterArity(missing).min, argumentStack);
                    }
                }
            }
            if (!unmatchedArguments.isEmpty()) {
                if (!isUnmatchedArgumentsAllowed()) { throw new UnmatchedArgumentException(CommandLine.this, unmatchedArguments); }
                if (tracer.isWarn()) { tracer.warn("Unmatched arguments: %s%n", unmatchedArguments); }
            }
        }

        private void processArguments(final List<CommandLine> parsedCommands,
                                      final Stack<String> args,
                                      final Collection<Field> required,
                                      final Set<Field> initialized,
                                      final String[] originalArgs) throws Exception {
            // arg must be one of:
            // 1. the "--" double dash separating options from positional arguments
            // 1. a stand-alone flag, like "-v" or "--verbose": no value required, must map to boolean or Boolean field
            // 2. a short option followed by an argument, like "-f file" or "-ffile": may map to any type of field
            // 3. a long option followed by an argument, like "-file out.txt" or "-file=out.txt"
            // 3. one or more remaining arguments without any associated options. Must be the last in the list.
            // 4. a combination of stand-alone options, like "-vxr". Equivalent to "-v -x -r", "-v true -x true -r true"
            // 5. a combination of stand-alone options and one option with an argument, like "-vxrffile"

            while (!args.isEmpty()) {
                String arg = args.pop();
                if (tracer.isDebug()) {tracer.debug("Processing argument '%s'. Remainder=%s%n", arg, reverse((Stack<String>) args.clone()));}

                // Double-dash separates options from positional arguments.
                // If found, then interpret the remaining args as positional parameters.
                if ("--".equals(arg)) {
                    tracer.info("Found end-of-options delimiter '--'. Treating remainder as positional parameters.%n");
                    processRemainderAsPositionalParameters(required, initialized, args);
                    return; // we are done
                }

                // if we find another command, we are done with the current command
                if (commands.containsKey(arg)) {
                    if (!isHelpRequested && !required.isEmpty()) { // ensure current command portion is valid
                        throw MissingParameterException.create(CommandLine.this, required, separator);
                    }
                    if (tracer.isDebug()) {tracer.debug("Found subcommand '%s' (%s)%n", arg, commands.get(arg).interpreter.command.getClass().getName());}
                    commands.get(arg).interpreter.parse(parsedCommands, args, originalArgs);
                    return; // remainder done by the command
                }

                // First try to interpret the argument as a single option (as opposed to a compact group of options).
                // A single option may be without option parameters, like "-v" or "--verbose" (a boolean value),
                // or an option may have one or more option parameters.
                // A parameter may be attached to the option.
                boolean paramAttachedToOption = false;
                final int separatorIndex = arg.indexOf(separator);
                if (separatorIndex > 0) {
                    final String key = arg.substring(0, separatorIndex);
                    // be greedy. Consume the whole arg as an option if possible.
                    if (optionName2Field.containsKey(key) && !optionName2Field.containsKey(arg)) {
                        paramAttachedToOption = true;
                        final String optionParam = arg.substring(separatorIndex + separator.length());
                        args.push(optionParam);
                        arg = key;
                        if (tracer.isDebug()) {tracer.debug("Separated '%s' option from '%s' option parameter%n", key, optionParam);}
                    } else if (tracer.isDebug()) {tracer.debug("'%s' contains separator '%s' but '%s' is not a known option%n", arg, separator, key);}
                } else if (tracer.isDebug()) {tracer.debug("'%s' cannot be separated into <option>%s<option-parameter>%n", arg, separator);}
                if (optionName2Field.containsKey(arg)) {
                    processStandaloneOption(required, initialized, arg, args, paramAttachedToOption);
                }
                // Compact (single-letter) options can be grouped with other options or with an argument.
                // only single-letter options can be combined with other options or with an argument
                else if (arg.length() > 2 && arg.startsWith("-")) {
                    if (tracer.isDebug()) {tracer.debug("Trying to process '%s' as clustered short options%n", arg, args);}
                    processClusteredShortOptions(required, initialized, arg, args);
                }
                // The argument could not be interpreted as an option.
                // We take this to mean that the remainder are positional arguments
                else {
                    args.push(arg);
                    if (tracer.isDebug()) {tracer.debug("Could not find option '%s', deciding whether to treat as unmatched option or positional parameter...%n", arg);}
                    if (resemblesOption(arg)) { handleUnmatchedArguments(args.pop()); continue; } // #149
                    if (tracer.isDebug()) {tracer.debug("No option named '%s' found. Processing remainder as positional parameters%n", arg);}
                    processPositionalParameter(required, initialized, args);
                }
            }
        }
        private boolean resemblesOption(final String arg) {
            int count = 0;
            for (final String optionName : optionName2Field.keySet()) {
                for (int i = 0; i < arg.length(); i++) {
                    if (optionName.length() > i && arg.charAt(i) == optionName.charAt(i)) { count++; } else { break; }
                }
            }
            final boolean result = count > 0 && count * 10 >= optionName2Field.size() * 9; // at least one prefix char in common with 9 out of 10 options
            if (tracer.isDebug()) {tracer.debug("%s %s an option: %d matching prefix chars out of %d option names%n", arg, (result ? "resembles" : "doesn't resemble"), count, optionName2Field.size());}
            return result;
        }
        private void handleUnmatchedArguments(final String arg) {final Stack<String> args = new Stack<>(); args.add(arg); handleUnmatchedArguments(args);}
        private void handleUnmatchedArguments(final Stack<String> args) {
            while (!args.isEmpty()) { unmatchedArguments.add(args.pop()); } // addAll would give args in reverse order
        }

        private void processRemainderAsPositionalParameters(final Collection<Field> required, final Set<Field> initialized, final Stack<String> args) throws Exception {
            while (!args.empty()) {
                processPositionalParameter(required, initialized, args);
            }
        }
        private void processPositionalParameter(final Collection<Field> required, final Set<Field> initialized, final Stack<String> args) throws Exception {
            if (tracer.isDebug()) {tracer.debug("Processing next arg as a positional parameter at index=%d. Remainder=%s%n", position, reverse((Stack<String>) args.clone()));}
            int consumed = 0;
            for (final Field positionalParam : positionalParametersFields) {
                final Range indexRange = Range.parameterIndex(positionalParam);
                if (!indexRange.contains(position)) {
                    continue;
                }
                @SuppressWarnings("unchecked")
                final
                Stack<String> argsCopy = (Stack<String>) args.clone();
                final Range arity = Range.parameterArity(positionalParam);
                if (tracer.isDebug()) {tracer.debug("Position %d is in index range %s. Trying to assign args to %s, arity=%s%n", position, indexRange, positionalParam, arity);}
                assertNoMissingParameters(positionalParam, arity.min, argsCopy);
                final int originalSize = argsCopy.size();
                applyOption(positionalParam, Parameters.class, arity, false, argsCopy, initialized, "args[" + indexRange + "] at position " + position);
                final int count = originalSize - argsCopy.size();
                if (count > 0) { required.remove(positionalParam); }
                consumed = Math.max(consumed, count);
            }
            // remove processed args from the stack
            for (int i = 0; i < consumed; i++) { args.pop(); }
            position += consumed;
            if (tracer.isDebug()) {tracer.debug("Consumed %d arguments, moving position to index %d.%n", consumed, position);}
            if (consumed == 0 && !args.isEmpty()) {
                handleUnmatchedArguments(args.pop());
            }
        }

        private void processStandaloneOption(final Collection<Field> required,
                                             final Set<Field> initialized,
                                             final String arg,
                                             final Stack<String> args,
                                             final boolean paramAttachedToKey) throws Exception {
            final Field field = optionName2Field.get(arg);
            required.remove(field);
            Range arity = Range.optionArity(field);
            if (paramAttachedToKey) {
                arity = arity.min(Math.max(1, arity.min)); // if key=value, minimum arity is at least 1
            }
            if (tracer.isDebug()) {tracer.debug("Found option named '%s': field %s, arity=%s%n", arg, field, arity);}
            applyOption(field, Option.class, arity, paramAttachedToKey, args, initialized, "option " + arg);
        }

        private void processClusteredShortOptions(final Collection<Field> required,
                                                  final Set<Field> initialized,
                                                  final String arg,
                                                  final Stack<String> args)
                throws Exception {
            final String prefix = arg.substring(0, 1);
            String cluster = arg.substring(1);
            boolean paramAttachedToOption = true;
            do {
                if (cluster.length() > 0 && singleCharOption2Field.containsKey(cluster.charAt(0))) {
                    final Field field = singleCharOption2Field.get(cluster.charAt(0));
                    Range arity = Range.optionArity(field);
                    final String argDescription = "option " + prefix + cluster.charAt(0);
                    if (tracer.isDebug()) {tracer.debug("Found option '%s%s' in %s: field %s, arity=%s%n", prefix, cluster.charAt(0), arg, field, arity);}
                    required.remove(field);
                    cluster = cluster.length() > 0 ? cluster.substring(1) : "";
                    paramAttachedToOption = cluster.length() > 0;
                    if (cluster.startsWith(separator)) {// attached with separator, like -f=FILE or -v=true
                        cluster = cluster.substring(separator.length());
                        arity = arity.min(Math.max(1, arity.min)); // if key=value, minimum arity is at least 1
                    }
                    if (arity.min > 0 && !empty(cluster)) {
                        if (tracer.isDebug()) {tracer.debug("Trying to process '%s' as option parameter%n", cluster);}
                    }
                    // arity may be >= 1, or
                    // arity <= 0 && !cluster.startsWith(separator)
                    // e.g., boolean @Option("-v", arity=0, varargs=true); arg "-rvTRUE", remainder cluster="TRUE"
                    if (!empty(cluster)) {
                        args.push(cluster); // interpret remainder as option parameter
                    }
                    final int consumed = applyOption(field, Option.class, arity, paramAttachedToOption, args, initialized, argDescription);
                    // only return if cluster (and maybe more) was consumed, otherwise continue do-while loop
                    if (empty(cluster) || consumed > 0 || args.isEmpty()) {
                        return;
                    }
                    cluster = args.pop();
                } else { // cluster is empty || cluster.charAt(0) is not a short option key
                    if (cluster.length() == 0) { // we finished parsing a group of short options like -rxv
                        return; // return normally and parse the next arg
                    }
                    // We get here when the remainder of the cluster group is neither an option,
                    // nor a parameter that the last option could consume.
                    if (arg.endsWith(cluster)) {
                        args.push(paramAttachedToOption ? prefix + cluster : cluster);
                        if (args.peek().equals(arg)) { // #149 be consistent between unmatched short and long options
                            if (tracer.isDebug()) {tracer.debug("Could not match any short options in %s, deciding whether to treat as unmatched option or positional parameter...%n", arg);}
                            if (resemblesOption(arg)) { handleUnmatchedArguments(args.pop()); return; } // #149
                            processPositionalParameter(required, initialized, args);
                            return;
                        }
                        // remainder was part of a clustered group that could not be completely parsed
                        if (tracer.isDebug()) {tracer.debug("No option found for %s in %s%n", cluster, arg);}
                        handleUnmatchedArguments(args.pop());
                    } else {
                        args.push(cluster);
                        if (tracer.isDebug()) {tracer.debug("%s is not an option parameter for %s%n", cluster, arg);}
                        processPositionalParameter(required, initialized, args);
                    }
                    return;
                }
            } while (true);
        }

        private int applyOption(final Field field,
                                final Class<?> annotation,
                                final Range arity,
                                final boolean valueAttachedToOption,
                                final Stack<String> args,
                                final Set<Field> initialized,
                                final String argDescription) throws Exception {
            updateHelpRequested(field);
            final int length = args.size();
            assertNoMissingParameters(field, arity.min, args);

            Class<?> cls = field.getType();
            if (cls.isArray()) {
                return applyValuesToArrayField(field, annotation, arity, args, cls, argDescription);
            }
            if (Collection.class.isAssignableFrom(cls)) {
                return applyValuesToCollectionField(field, annotation, arity, args, cls, argDescription);
            }
            if (Map.class.isAssignableFrom(cls)) {
                return applyValuesToMapField(field, annotation, arity, args, cls, argDescription);
            }
            cls = getTypeAttribute(field)[0]; // field may be interface/abstract type, use annotation to get concrete type
            return applyValueToSingleValuedField(field, arity, args, cls, initialized, argDescription);
        }

        private int applyValueToSingleValuedField(final Field field,
                                                  final Range arity,
                                                  final Stack<String> args,
                                                  final Class<?> cls,
                                                  final Set<Field> initialized,
                                                  final String argDescription) throws Exception {
            final boolean noMoreValues = args.isEmpty();
            String value = args.isEmpty() ? null : trim(args.pop()); // unquote the value
            int result = arity.min; // the number or args we need to consume

            // special logic for booleans: BooleanConverter accepts only "true" or "false".
            if ((cls == Boolean.class || cls == Boolean.TYPE) && arity.min <= 0) {

                // boolean option with arity = 0..1 or 0..*: value MAY be a param
                if (arity.max > 0 && ("true".equalsIgnoreCase(value) || "false".equalsIgnoreCase(value))) {
                    result = 1;            // if it is a varargs we only consume 1 argument if it is a boolean value
                } else {
                    if (value != null) {
                        args.push(value); // we don't consume the value
                    }
                    final Boolean currentValue = (Boolean) field.get(command);
                    value = String.valueOf(currentValue == null ? true : !currentValue); // #147 toggle existing boolean value
                }
            }
            if (noMoreValues && value == null) {
                return 0;
            }
            final ITypeConverter<?> converter = getTypeConverter(cls, field);
            final Object newValue = tryConvert(field, -1, converter, value, cls);
            final Object oldValue = field.get(command);
            TraceLevel level = TraceLevel.INFO;
            String traceMessage = "Setting %s field '%s.%s' to '%5$s' (was '%4$s') for %6$s%n";
            if (initialized != null) {
                if (initialized.contains(field)) {
                    if (!isOverwrittenOptionsAllowed()) {
                        throw new OverwrittenOptionException(CommandLine.this, optionDescription("", field, 0) +  " should be specified only once");
                    }
                    level = TraceLevel.WARN;
                    traceMessage = "Overwriting %s field '%s.%s' value '%s' with '%s' for %s%n";
                }
                initialized.add(field);
            }
            if (tracer.level.isEnabled(level)) { level.print(tracer, traceMessage, field.getType().getSimpleName(),
                        field.getDeclaringClass().getSimpleName(), field.getName(), String.valueOf(oldValue), String.valueOf(newValue), argDescription);
            }
            field.set(command, newValue);
            return result;
        }
        private int applyValuesToMapField(final Field field,
                                          final Class<?> annotation,
                                          final Range arity,
                                          final Stack<String> args,
                                          final Class<?> cls,
                                          final String argDescription) throws Exception {
            final Class<?>[] classes = getTypeAttribute(field);
            if (classes.length < 2) { throw new ParameterException(CommandLine.this, "Field " + field + " needs two types (one for the map key, one for the value) but only has " + classes.length + " types configured."); }
            final ITypeConverter<?> keyConverter   = getTypeConverter(classes[0], field);
            final ITypeConverter<?> valueConverter = getTypeConverter(classes[1], field);
            Map<Object, Object> result = (Map<Object, Object>) field.get(command);
            if (result == null) {
                result = createMap(cls);
                field.set(command, result);
            }
            final int originalSize = result.size();
            consumeMapArguments(field, arity, args, classes, keyConverter, valueConverter, result, argDescription);
            return result.size() - originalSize;
        }

        private void consumeMapArguments(final Field field,
                                         final Range arity,
                                         final Stack<String> args,
                                         final Class<?>[] classes,
                                         final ITypeConverter<?> keyConverter,
                                         final ITypeConverter<?> valueConverter,
                                         final Map<Object, Object> result,
                                         final String argDescription) throws Exception {
            // first do the arity.min mandatory parameters
            for (int i = 0; i < arity.min; i++) {
                consumeOneMapArgument(field, arity, args, classes, keyConverter, valueConverter, result, i, argDescription);
            }
            // now process the varargs if any
            for (int i = arity.min; i < arity.max && !args.isEmpty(); i++) {
                if (!field.isAnnotationPresent(Parameters.class)) {
                    if (commands.containsKey(args.peek()) || isOption(args.peek())) {
                        return;
                    }
                }
                consumeOneMapArgument(field, arity, args, classes, keyConverter, valueConverter, result, i, argDescription);
            }
        }

        private void consumeOneMapArgument(final Field field,
                                           final Range arity,
                                           final Stack<String> args,
                                           final Class<?>[] classes,
                                           final ITypeConverter<?> keyConverter, final ITypeConverter<?> valueConverter,
                                           final Map<Object, Object> result,
                                           final int index,
                                           final String argDescription) throws Exception {
            final String[] values = split(trim(args.pop()), field);
            for (final String value : values) {
                final String[] keyValue = value.split("=");
                if (keyValue.length < 2) {
                    final String splitRegex = splitRegex(field);
                    if (splitRegex.length() == 0) {
                        throw new ParameterException(CommandLine.this, "Value for option " + optionDescription("", field,
                                0) + " should be in KEY=VALUE format but was " + value);
                    } else {
                        throw new ParameterException(CommandLine.this, "Value for option " + optionDescription("", field,
                                0) + " should be in KEY=VALUE[" + splitRegex + "KEY=VALUE]... format but was " + value);
                    }
                }
                final Object mapKey =   tryConvert(field, index, keyConverter,   keyValue[0], classes[0]);
                final Object mapValue = tryConvert(field, index, valueConverter, keyValue[1], classes[1]);
                result.put(mapKey, mapValue);
                if (tracer.isInfo()) {tracer.info("Putting [%s : %s] in %s<%s, %s> field '%s.%s' for %s%n", String.valueOf(mapKey), String.valueOf(mapValue),
                        result.getClass().getSimpleName(), classes[0].getSimpleName(), classes[1].getSimpleName(), field.getDeclaringClass().getSimpleName(), field.getName(), argDescription);}
            }
        }

        private void checkMaxArityExceeded(final Range arity, final int remainder, final Field field, final String[] values) {
            if (values.length <= remainder) { return; }
            final String desc = arity.max == remainder ? "" + remainder : arity + ", remainder=" + remainder;
            throw new MaxValuesforFieldExceededException(CommandLine.this, optionDescription("", field, -1) +
                    " max number of values (" + arity.max + ") exceeded: remainder is " + remainder + " but " +
                    values.length + " values were specified: " + Arrays.toString(values));
        }

        private int applyValuesToArrayField(final Field field,
                                            final Class<?> annotation,
                                            final Range arity,
                                            final Stack<String> args,
                                            final Class<?> cls,
                                            final String argDescription) throws Exception {
            final Object existing = field.get(command);
            final int length = existing == null ? 0 : Array.getLength(existing);
            final Class<?> type = getTypeAttribute(field)[0];
            final List<Object> converted = consumeArguments(field, annotation, arity, args, type, length, argDescription);
            final List<Object> newValues = new ArrayList<>();
            for (int i = 0; i < length; i++) {
                newValues.add(Array.get(existing, i));
            }
            for (final Object obj : converted) {
                if (obj instanceof Collection<?>) {
                    newValues.addAll((Collection<?>) obj);
                } else {
                    newValues.add(obj);
                }
            }
            final Object array = Array.newInstance(type, newValues.size());
            field.set(command, array);
            for (int i = 0; i < newValues.size(); i++) {
                Array.set(array, i, newValues.get(i));
            }
            return converted.size(); // return how many args were consumed
        }

        @SuppressWarnings("unchecked")
        private int applyValuesToCollectionField(final Field field,
                                                 final Class<?> annotation,
                                                 final Range arity,
                                                 final Stack<String> args,
                                                 final Class<?> cls,
                                                 final String argDescription) throws Exception {
            Collection<Object> collection = (Collection<Object>) field.get(command);
            final Class<?> type = getTypeAttribute(field)[0];
            final int length = collection == null ? 0 : collection.size();
            final List<Object> converted = consumeArguments(field, annotation, arity, args, type, length, argDescription);
            if (collection == null) {
                collection = createCollection(cls);
                field.set(command, collection);
            }
            for (final Object element : converted) {
                if (element instanceof Collection<?>) {
                    collection.addAll((Collection<?>) element);
                } else {
                    collection.add(element);
                }
            }
            return converted.size();
        }

        private List<Object> consumeArguments(final Field field,
                                              final Class<?> annotation,
                                              final Range arity,
                                              final Stack<String> args,
                                              final Class<?> type,
                                              final int originalSize,
                                              final String argDescription) throws Exception {
            final List<Object> result = new ArrayList<>();

            // first do the arity.min mandatory parameters
            for (int i = 0; i < arity.min; i++) {
                consumeOneArgument(field, arity, args, type, result, i, originalSize, argDescription);
            }
            // now process the varargs if any
            for (int i = arity.min; i < arity.max && !args.isEmpty(); i++) {
                if (annotation != Parameters.class) { // for vararg Options, we stop if we encounter '--', a command, or another option
                    if (commands.containsKey(args.peek()) || isOption(args.peek())) {
                        return result;
                    }
                }
                consumeOneArgument(field, arity, args, type, result, i, originalSize, argDescription);
            }
            return result;
        }

        private int consumeOneArgument(final Field field,
                                       final Range arity,
                                       final Stack<String> args,
                                       final Class<?> type,
                                       final List<Object> result,
                                       int index,
                                       final int originalSize,
                                       final String argDescription) throws Exception {
            final String[] values = split(trim(args.pop()), field);
            final ITypeConverter<?> converter = getTypeConverter(type, field);

            for (int j = 0; j < values.length; j++) {
                result.add(tryConvert(field, index, converter, values[j], type));
                if (tracer.isInfo()) {
                    if (field.getType().isArray()) {
                        tracer.info("Adding [%s] to %s[] field '%s.%s' for %s%n", String.valueOf(result.get(result.size() - 1)), type.getSimpleName(), field.getDeclaringClass().getSimpleName(), field.getName(), argDescription);
                    } else {
                        tracer.info("Adding [%s] to %s<%s> field '%s.%s' for %s%n", String.valueOf(result.get(result.size() - 1)), field.getType().getSimpleName(), type.getSimpleName(), field.getDeclaringClass().getSimpleName(), field.getName(), argDescription);
                    }
                }
            }
            //checkMaxArityExceeded(arity, max, field, values);
            return ++index;
        }

        private String splitRegex(final Field field) {
            if (field.isAnnotationPresent(Option.class))     { return field.getAnnotation(Option.class).split(); }
            if (field.isAnnotationPresent(Parameters.class)) { return field.getAnnotation(Parameters.class).split(); }
            return "";
        }
        private String[] split(final String value, final Field field) {
            final String regex = splitRegex(field);
            return regex.length() == 0 ? new String[] {value} : value.split(regex);
        }

        /**
         * Called when parsing varargs parameters for a multi-value option.
         * When an option is encountered, the remainder should not be interpreted as vararg elements.
         * @param arg the string to determine whether it is an option or not
         * @return true if it is an option, false otherwise
         */
        private boolean isOption(final String arg) {
            if ("--".equals(arg)) {
                return true;
            }
            // not just arg prefix: we may be in the middle of parsing -xrvfFILE
            if (optionName2Field.containsKey(arg)) { // -v or -f or --file (not attached to param or other option)
                return true;
            }
            final int separatorIndex = arg.indexOf(separator);
            if (separatorIndex > 0) { // -f=FILE or --file==FILE (attached to param via separator)
                if (optionName2Field.containsKey(arg.substring(0, separatorIndex))) {
                    return true;
                }
            }
            return (arg.length() > 2 && arg.startsWith("-") && singleCharOption2Field.containsKey(arg.charAt(1)));
        }
        private Object tryConvert(final Field field, final int index, final ITypeConverter<?> converter, final String value, final Class<?> type)
                throws Exception {
            try {
                return converter.convert(value);
            } catch (final TypeConversionException ex) {
                throw new ParameterException(CommandLine.this, ex.getMessage() + optionDescription(" for ", field, index));
            } catch (final Exception other) {
                final String desc = optionDescription(" for ", field, index) + ": " + other;
                throw new ParameterException(CommandLine.this, "Could not convert '" + value + "' to " + type.getSimpleName() + desc, other);
            }
        }

        private String optionDescription(final String prefix, final Field field, final int index) {
            final Help.IParamLabelRenderer labelRenderer = Help.createMinimalParamLabelRenderer();
            String desc = "";
            if (field.isAnnotationPresent(Option.class)) {
                desc = prefix + "option '" + field.getAnnotation(Option.class).names()[0] + "'";
                if (index >= 0) {
                    final Range arity = Range.optionArity(field);
                    if (arity.max > 1) {
                        desc += " at index " + index;
                    }
                    desc += " (" + labelRenderer.renderParameterLabel(field, Help.Ansi.OFF, Collections.<IStyle>emptyList()) + ")";
                }
            } else if (field.isAnnotationPresent(Parameters.class)) {
                final Range indexRange = Range.parameterIndex(field);
                final Text label = labelRenderer.renderParameterLabel(field, Help.Ansi.OFF, Collections.<IStyle>emptyList());
                desc = prefix + "positional parameter at index " + indexRange + " (" + label + ")";
            }
            return desc;
        }

        private boolean isAnyHelpRequested() { return isHelpRequested || versionHelpRequested || usageHelpRequested; }

        private void updateHelpRequested(final Field field) {
            if (field.isAnnotationPresent(Option.class)) {
                isHelpRequested                       |= is(field, "help", field.getAnnotation(Option.class).help());
                CommandLine.this.versionHelpRequested |= is(field, "versionHelp", field.getAnnotation(Option.class).versionHelp());
                CommandLine.this.usageHelpRequested   |= is(field, "usageHelp", field.getAnnotation(Option.class).usageHelp());
            }
        }
        private boolean is(final Field f, final String description, final boolean value) {
            if (value) { if (tracer.isInfo()) {tracer.info("Field '%s.%s' has '%s' annotation: not validating required fields%n", f.getDeclaringClass().getSimpleName(), f.getName(), description); }}
            return value;
        }
        @SuppressWarnings("unchecked")
        private Collection<Object> createCollection(final Class<?> collectionClass) throws Exception {
            if (collectionClass.isInterface()) {
                if (SortedSet.class.isAssignableFrom(collectionClass)) {
                    return new TreeSet<>();
                } else if (Set.class.isAssignableFrom(collectionClass)) {
                    return new LinkedHashSet<>();
                } else if (Queue.class.isAssignableFrom(collectionClass)) {
                    return new LinkedList<>(); // ArrayDeque is only available since 1.6
                }
                return new ArrayList<>();
            }
            // custom Collection implementation class must have default constructor
            return (Collection<Object>) collectionClass.newInstance();
        }
        private Map<Object, Object> createMap(final Class<?> mapClass) throws Exception {
            try { // if it is an implementation class, instantiate it
                return (Map<Object, Object>) mapClass.newInstance();
            } catch (final Exception ignored) {}
            return new LinkedHashMap<>();
        }
        private ITypeConverter<?> getTypeConverter(final Class<?> type, final Field field) {
            final ITypeConverter<?> result = converterRegistry.get(type);
            if (result != null) {
                return result;
            }
            if (type.isEnum()) {
                return new ITypeConverter<Object>() {
                    @Override
                    @SuppressWarnings("unchecked")
                    public Object convert(final String value) throws Exception {
                        return Enum.valueOf((Class<Enum>) type, value);
                    }
                };
            }
            throw new MissingTypeConverterException(CommandLine.this, "No TypeConverter registered for " + type.getName() + " of field " + field);
        }

        private void assertNoMissingParameters(final Field field, final int arity, final Stack<String> args) {
            if (arity > args.size()) {
                if (arity == 1) {
                    if (field.isAnnotationPresent(Option.class)) {
                        throw new MissingParameterException(CommandLine.this, "Missing required parameter for " +
                                optionDescription("", field, 0));
                    }
                    final Range indexRange = Range.parameterIndex(field);
                    final Help.IParamLabelRenderer labelRenderer = Help.createMinimalParamLabelRenderer();
                    String sep = "";
                    String names = "";
                    int count = 0;
                    for (int i = indexRange.min; i < positionalParametersFields.size(); i++) {
                        if (Range.parameterArity(positionalParametersFields.get(i)).min > 0) {
                            names += sep + labelRenderer.renderParameterLabel(positionalParametersFields.get(i),
                                    Help.Ansi.OFF, Collections.<IStyle>emptyList());
                            sep = ", ";
                            count++;
                        }
                    }
                    String msg = "Missing required parameter";
                    final Range paramArity = Range.parameterArity(field);
                    if (paramArity.isVariable) {
                        msg += "s at positions " + indexRange + ": ";
                    } else {
                        msg += (count > 1 ? "s: " : ": ");
                    }
                    throw new MissingParameterException(CommandLine.this, msg + names);
                }
                if (args.isEmpty()) {
                    throw new MissingParameterException(CommandLine.this, optionDescription("", field, 0) +
                            " requires at least " + arity + " values, but none were specified.");
                }
                throw new MissingParameterException(CommandLine.this, optionDescription("", field, 0) +
                        " requires at least " + arity + " values, but only " + args.size() + " were specified: " + reverse(args));
            }
        }
        private String trim(final String value) {
            return unquote(value);
        }

        private String unquote(final String value) {
            return value == null
                    ? null
                    : (value.length() > 1 && value.startsWith("\"") && value.endsWith("\""))
                        ? value.substring(1, value.length() - 1)
                        : value;
        }
    }
    private static class PositionalParametersSorter implements Comparator<Field> {
        @Override
        public int compare(final Field o1, final Field o2) {
            final int result = Range.parameterIndex(o1).compareTo(Range.parameterIndex(o2));
            return (result == 0) ? Range.parameterArity(o1).compareTo(Range.parameterArity(o2)) : result;
        }
    }
    /**
     * Inner class to group the built-in {@link ITypeConverter} implementations.
     */
    private static class BuiltIn {
        static class PathConverter implements ITypeConverter<Path> {
            @Override public Path convert(final String value) { return Paths.get(value); }
        }
        static class StringConverter implements ITypeConverter<String> {
            @Override
            public String convert(final String value) { return value; }
        }
        static class StringBuilderConverter implements ITypeConverter<StringBuilder> {
            @Override
            public StringBuilder convert(final String value) { return new StringBuilder(value); }
        }
        static class CharSequenceConverter implements ITypeConverter<CharSequence> {
            @Override
            public String convert(final String value) { return value; }
        }
        /** Converts text to a {@code Byte} by delegating to {@link Byte#valueOf(String)}.*/
        static class ByteConverter implements ITypeConverter<Byte> {
            @Override
            public Byte convert(final String value) { return Byte.valueOf(value); }
        }
        /** Converts {@code "true"} or {@code "false"} to a {@code Boolean}. Other values result in a ParameterException.*/
        static class BooleanConverter implements ITypeConverter<Boolean> {
            @Override
            public Boolean convert(final String value) {
                if ("true".equalsIgnoreCase(value) || "false".equalsIgnoreCase(value)) {
                    return Boolean.parseBoolean(value);
                } else {
                    throw new TypeConversionException("'" + value + "' is not a boolean");
                }
            }
        }
        static class CharacterConverter implements ITypeConverter<Character> {
            @Override
            public Character convert(final String value) {
                if (value.length() > 1) {
                    throw new TypeConversionException("'" + value + "' is not a single character");
                }
                return value.charAt(0);
            }
        }
        /** Converts text to a {@code Short} by delegating to {@link Short#valueOf(String)}.*/
        static class ShortConverter implements ITypeConverter<Short> {
            @Override
            public Short convert(final String value) { return Short.valueOf(value); }
        }
        /** Converts text to an {@code Integer} by delegating to {@link Integer#valueOf(String)}.*/
        static class IntegerConverter implements ITypeConverter<Integer> {
            @Override
            public Integer convert(final String value) { return Integer.valueOf(value); }
        }
        /** Converts text to a {@code Long} by delegating to {@link Long#valueOf(String)}.*/
        static class LongConverter implements ITypeConverter<Long> {
            @Override
            public Long convert(final String value) { return Long.valueOf(value); }
        }
        static class FloatConverter implements ITypeConverter<Float> {
            @Override
            public Float convert(final String value) { return Float.valueOf(value); }
        }
        static class DoubleConverter implements ITypeConverter<Double> {
            @Override
            public Double convert(final String value) { return Double.valueOf(value); }
        }
        static class FileConverter implements ITypeConverter<File> {
            @Override
            public File convert(final String value) { return new File(value); }
        }
        static class URLConverter implements ITypeConverter<URL> {
            @Override
            public URL convert(final String value) throws MalformedURLException { return new URL(value); }
        }
        static class URIConverter implements ITypeConverter<URI> {
            @Override
            public URI convert(final String value) throws URISyntaxException { return new URI(value); }
        }
        /** Converts text in {@code yyyy-mm-dd} format to a {@code java.util.Date}. ParameterException on failure. */
        static class ISO8601DateConverter implements ITypeConverter<Date> {
            @Override
            public Date convert(final String value) {
                try {
                    return new SimpleDateFormat("yyyy-MM-dd").parse(value);
                } catch (final ParseException e) {
                    throw new TypeConversionException("'" + value + "' is not a yyyy-MM-dd date");
                }
            }
        }
        /** Converts text in any of the following formats to a {@code java.sql.Time}: {@code HH:mm}, {@code HH:mm:ss},
         * {@code HH:mm:ss.SSS}, {@code HH:mm:ss,SSS}. Other formats result in a ParameterException. */
        static class ISO8601TimeConverter implements ITypeConverter<Time> {
            @Override
            public Time convert(final String value) {
                try {
                    if (value.length() <= 5) {
                        return new Time(new SimpleDateFormat("HH:mm").parse(value).getTime());
                    } else if (value.length() <= 8) {
                        return new Time(new SimpleDateFormat("HH:mm:ss").parse(value).getTime());
                    } else if (value.length() <= 12) {
                        try {
                            return new Time(new SimpleDateFormat("HH:mm:ss.SSS").parse(value).getTime());
                        } catch (final ParseException e2) {
                            return new Time(new SimpleDateFormat("HH:mm:ss,SSS").parse(value).getTime());
                        }
                    }
                } catch (final ParseException ignored) {
                    // ignored because we throw a ParameterException below
                }
                throw new TypeConversionException("'" + value + "' is not a HH:mm[:ss[.SSS]] time");
            }
        }
        static class BigDecimalConverter implements ITypeConverter<BigDecimal> {
            @Override
            public BigDecimal convert(final String value) { return new BigDecimal(value); }
        }
        static class BigIntegerConverter implements ITypeConverter<BigInteger> {
            @Override
            public BigInteger convert(final String value) { return new BigInteger(value); }
        }
        static class CharsetConverter implements ITypeConverter<Charset> {
            @Override
            public Charset convert(final String s) { return Charset.forName(s); }
        }
        /** Converts text to a {@code InetAddress} by delegating to {@link InetAddress#getByName(String)}. */
        static class InetAddressConverter implements ITypeConverter<InetAddress> {
            @Override
            public InetAddress convert(final String s) throws Exception { return InetAddress.getByName(s); }
        }
        static class PatternConverter implements ITypeConverter<Pattern> {
            @Override
            public Pattern convert(final String s) { return Pattern.compile(s); }
        }
        static class UUIDConverter implements ITypeConverter<UUID> {
            @Override
            public UUID convert(final String s) throws Exception { return UUID.fromString(s); }
        }
        private BuiltIn() {} // private constructor: never instantiate
    }

    /**
     * A collection of methods and inner classes that provide fine-grained control over the contents and layout of
     * the usage help message to display to end users when help is requested or invalid input values were specified.
     * <h3>Layered API</h3>
     * <p>The {@link Command} annotation provides the easiest way to customize usage help messages. See
     * the <a href="https://remkop.github.io/picocli/index.html#_usage_help">Manual</a> for details.</p>
     * <p>This Help class provides high-level functions to create sections of the usage help message and headings
     * for these sections. Instead of calling the {@link CommandLine#usage(PrintStream, CommandLine.Help.ColorScheme)}
     * method, application authors may want to create a custom usage help message by reorganizing sections in a
     * different order and/or adding custom sections.</p>
     * <p>Finally, the Help class contains inner classes and interfaces that can be used to create custom help messages.</p>
     * <h4>IOptionRenderer and IParameterRenderer</h4>
     * <p>Renders a field annotated with {@link Option} or {@link Parameters} to an array of {@link Text} values.
     * By default, these values are</p><ul>
     * <li>mandatory marker character (if the option/parameter is {@link Option#required() required})</li>
     * <li>short option name (empty for parameters)</li>
     * <li>comma or empty (empty for parameters)</li>
     * <li>long option names (the parameter {@link IParamLabelRenderer label} for parameters)</li>
     * <li>description</li>
     * </ul>
     * <p>Other components rely on this ordering.</p>
     * <h4>Layout</h4>
     * <p>Delegates to the renderers to create {@link Text} values for the annotated fields, and uses a
     * {@link TextTable} to display these values in tabular format. Layout is responsible for deciding which values
     * to display where in the table. By default, Layout shows one option or parameter per table row.</p>
     * <h4>TextTable</h4>
     * <p>Responsible for spacing out {@link Text} values according to the {@link Column} definitions the table was
     * created with. Columns have a width, indentation, and an overflow policy that decides what to do if a value is
     * longer than the column's width.</p>
     * <h4>Text</h4>
     * <p>Encapsulates rich text with styles and colors in a way that other components like {@link TextTable} are
     * unaware of the embedded ANSI escape codes.</p>
     */
    public static class Help {
        /** Constant String holding the default program name: {@value} */
        protected static final String DEFAULT_COMMAND_NAME = "<main class>";

        /** Constant String holding the default string that separates options from option parameters: {@value} */
        protected static final String DEFAULT_SEPARATOR = "=";

        private final static int usageHelpWidth = 80;
        private final static int optionsColumnWidth = 2 + 2 + 1 + 24;
        private final Object command;
        private final Map<String, Help> commands = new LinkedHashMap<>();
        final ColorScheme colorScheme;

        /** Immutable list of fields annotated with {@link Option}, in declaration order. */
        public final List<Field> optionFields;

        /** Immutable list of fields annotated with {@link Parameters}, or an empty list if no such field exists. */
        public final List<Field> positionalParametersFields;

        /** The String to use as the separator between options and option parameters. {@code "="} by default,
         * initialized from {@link Command#separator()} if defined.
         * @see #parameterLabelRenderer */
        public String separator;

        /** The String to use as the program name in the synopsis line of the help message.
         * {@link #DEFAULT_COMMAND_NAME} by default, initialized from {@link Command#name()} if defined. */
        public String commandName = DEFAULT_COMMAND_NAME;

        /** Optional text lines to use as the description of the help message, displayed between the synopsis and the
         * options list. Initialized from {@link Command#description()} if the {@code Command} annotation is present,
         * otherwise this is an empty array and the help message has no description.
         * Applications may programmatically set this field to create a custom help message. */
        public String[] description = {};

        /** Optional custom synopsis lines to use instead of the auto-generated synopsis.
         * Initialized from {@link Command#customSynopsis()} if the {@code Command} annotation is present,
         * otherwise this is an empty array and the synopsis is generated.
         * Applications may programmatically set this field to create a custom help message. */
        public String[] customSynopsis = {};

        /** Optional header lines displayed at the top of the help message. For subcommands, the first header line is
         * displayed in the list of commands. Values are initialized from {@link Command#header()}
         * if the {@code Command} annotation is present, otherwise this is an empty array and the help message has no
         * header. Applications may programmatically set this field to create a custom help message. */
        public String[] header = {};

        /** Optional footer text lines displayed at the bottom of the help message. Initialized from
         * {@link Command#footer()} if the {@code Command} annotation is present, otherwise this is an empty array and
         * the help message has no footer.
         * Applications may programmatically set this field to create a custom help message. */
        public String[] footer = {};

        /** Option and positional parameter value label renderer used for the synopsis line(s) and the option list.
         * By default initialized to the result of {@link #createDefaultParamLabelRenderer()}, which takes a snapshot
         * of the {@link #separator} at construction time. If the separator is modified after Help construction, you
         * may need to re-initialize this field by calling {@link #createDefaultParamLabelRenderer()} again. */
        public IParamLabelRenderer parameterLabelRenderer;

        /** If {@code true}, the synopsis line(s) will show an abbreviated synopsis without detailed option names. */
        public Boolean abbreviateSynopsis;

        /** If {@code true}, the options list is sorted alphabetically. */
        public Boolean sortOptions;

        /** If {@code true}, the options list will show default values for all options except booleans. */
        public Boolean showDefaultValues;

        /** Character used to prefix required options in the options list. */
        public Character requiredOptionMarker;

        /** Optional heading preceding the header section. Initialized from {@link Command#headerHeading()}, or null. */
        public String headerHeading;

        /** Optional heading preceding the synopsis. Initialized from {@link Command#synopsisHeading()}, {@code "Usage: "} by default. */
        public String synopsisHeading;

        /** Optional heading preceding the description section. Initialized from {@link Command#descriptionHeading()}, or null. */
        public String descriptionHeading;

        /** Optional heading preceding the parameter list. Initialized from {@link Command#parameterListHeading()}, or null. */
        public String parameterListHeading;

        /** Optional heading preceding the options list. Initialized from {@link Command#optionListHeading()}, or null. */
        public String optionListHeading;

        /** Optional heading preceding the subcommand list. Initialized from {@link Command#commandListHeading()}. {@code "Commands:%n"} by default. */
        public String commandListHeading;

        /** Optional heading preceding the footer section. Initialized from {@link Command#footerHeading()}, or null. */
        public String footerHeading;

        /** Constructs a new {@code Help} instance with a default color scheme, initialized from annotatations
         * on the specified class and superclasses.
         * @param command the annotated object to create usage help for */
        public Help(final Object command) {
            this(command, Ansi.AUTO);
        }

        /** Constructs a new {@code Help} instance with a default color scheme, initialized from annotatations
         * on the specified class and superclasses.
         * @param command the annotated object to create usage help for
         * @param ansi whether to emit ANSI escape codes or not */
        public Help(final Object command, final Ansi ansi) {
            this(command, defaultColorScheme(ansi));
        }

        /** Constructs a new {@code Help} instance with the specified color scheme, initialized from annotatations
         * on the specified class and superclasses.
         * @param command the annotated object to create usage help for
         * @param colorScheme the color scheme to use */
        public Help(final Object command, final ColorScheme colorScheme) {
            this.command = Assert.notNull(command, "command");
            this.colorScheme = Assert.notNull(colorScheme, "colorScheme").applySystemProperties();
            final List<Field> options = new ArrayList<>();
            final List<Field> operands = new ArrayList<>();
            Class<?> cls = command.getClass();
            while (cls != null) {
                for (final Field field : cls.getDeclaredFields()) {
                    field.setAccessible(true);
                    if (field.isAnnotationPresent(Option.class)) {
                        final Option option = field.getAnnotation(Option.class);
                        if (!option.hidden()) { // hidden options should not appear in usage help
                            // TODO remember longest concatenated option string length (issue #45)
                            options.add(field);
                        }
                    }
                    if (field.isAnnotationPresent(Parameters.class)) {
                        operands.add(field);
                    }
                }
                // superclass values should not overwrite values if both class and superclass have a @Command annotation
                if (cls.isAnnotationPresent(Command.class)) {
                    final Command cmd = cls.getAnnotation(Command.class);
                    if (DEFAULT_COMMAND_NAME.equals(commandName)) {
                        commandName = cmd.name();
                    }
                    separator = (separator == null) ? cmd.separator() : separator;
                    abbreviateSynopsis = (abbreviateSynopsis == null) ? cmd.abbreviateSynopsis() : abbreviateSynopsis;
                    sortOptions = (sortOptions == null) ? cmd.sortOptions() : sortOptions;
                    requiredOptionMarker = (requiredOptionMarker == null) ? cmd.requiredOptionMarker() : requiredOptionMarker;
                    showDefaultValues = (showDefaultValues == null) ? cmd.showDefaultValues() : showDefaultValues;
                    customSynopsis = empty(customSynopsis) ? cmd.customSynopsis() : customSynopsis;
                    description = empty(description) ? cmd.description() : description;
                    header = empty(header) ? cmd.header() : header;
                    footer = empty(footer) ? cmd.footer() : footer;
                    headerHeading = empty(headerHeading) ? cmd.headerHeading() : headerHeading;
                    synopsisHeading = empty(synopsisHeading) || "Usage: ".equals(synopsisHeading) ? cmd.synopsisHeading() : synopsisHeading;
                    descriptionHeading = empty(descriptionHeading) ? cmd.descriptionHeading() : descriptionHeading;
                    parameterListHeading = empty(parameterListHeading) ? cmd.parameterListHeading() : parameterListHeading;
                    optionListHeading = empty(optionListHeading) ? cmd.optionListHeading() : optionListHeading;
                    commandListHeading = empty(commandListHeading) || "Commands:%n".equals(commandListHeading) ? cmd.commandListHeading() : commandListHeading;
                    footerHeading = empty(footerHeading) ? cmd.footerHeading() : footerHeading;
                }
                cls = cls.getSuperclass();
            }
            sortOptions =          (sortOptions == null)          ? true : sortOptions;
            abbreviateSynopsis =   (abbreviateSynopsis == null)   ? false : abbreviateSynopsis;
            requiredOptionMarker = (requiredOptionMarker == null) ? ' ' : requiredOptionMarker;
            showDefaultValues =    (showDefaultValues == null)    ? false : showDefaultValues;
            synopsisHeading =      (synopsisHeading == null)      ? "Usage: " : synopsisHeading;
            commandListHeading =   (commandListHeading == null)   ? "Commands:%n" : commandListHeading;
            separator =            (separator == null)            ? DEFAULT_SEPARATOR : separator;
            parameterLabelRenderer = createDefaultParamLabelRenderer(); // uses help separator
            Collections.sort(operands, new PositionalParametersSorter());
            positionalParametersFields = Collections.unmodifiableList(operands);
            optionFields                 = Collections.unmodifiableList(options);
        }

        /** Registers all specified subcommands with this Help.
         * @param commands maps the command names to the associated CommandLine object
         * @return this Help instance (for method chaining)
         * @see CommandLine#getSubcommands()
         */
        public Help addAllSubcommands(final Map<String, CommandLine> commands) {
            if (commands != null) {
                for (final Map.Entry<String, CommandLine> entry : commands.entrySet()) {
                    addSubcommand(entry.getKey(), entry.getValue().getCommand());
                }
            }
            return this;
        }

        /** Registers the specified subcommand with this Help.
         * @param commandName the name of the subcommand to display in the usage message
         * @param command the annotated object to get more information from
         * @return this Help instance (for method chaining)
         */
        public Help addSubcommand(final String commandName, final Object command) {
            commands.put(commandName, new Help(command));
            return this;
        }

        /** Returns a synopsis for the command without reserving space for the synopsis heading.
         * @return a synopsis
         * @see #abbreviatedSynopsis()
         * @see #detailedSynopsis(Comparator, boolean)
         * @deprecated use {@link #synopsis(int)} instead
         */
        @Deprecated
        public String synopsis() { return synopsis(0); }

        /**
         * Returns a synopsis for the command, reserving the specified space for the synopsis heading.
         * @param synopsisHeadingLength the length of the synopsis heading that will be displayed on the same line
         * @return a synopsis
         * @see #abbreviatedSynopsis()
         * @see #detailedSynopsis(Comparator, boolean)
         * @see #synopsisHeading
         */
        public String synopsis(final int synopsisHeadingLength) {
            if (!empty(customSynopsis)) { return customSynopsis(); }
            return abbreviateSynopsis ? abbreviatedSynopsis()
                    : detailedSynopsis(synopsisHeadingLength, createShortOptionArityAndNameComparator(), true);
        }

        /** Generates a generic synopsis like {@code <command name> [OPTIONS] [PARAM1 [PARAM2]...]}, omitting parts
         * that don't apply to the command (e.g., does not show [OPTIONS] if the command has no options).
         * @return a generic synopsis */
        public String abbreviatedSynopsis() {
            final StringBuilder sb = new StringBuilder();
            if (!optionFields.isEmpty()) { // only show if annotated object actually has options
                sb.append(" [OPTIONS]");
            }
            // sb.append(" [--] "); // implied
            for (final Field positionalParam : positionalParametersFields) {
                if (!positionalParam.getAnnotation(Parameters.class).hidden()) {
                    sb.append(' ').append(parameterLabelRenderer.renderParameterLabel(positionalParam, ansi(), colorScheme.parameterStyles));
                }
            }
            return colorScheme.commandText(commandName).toString()
                    + (sb.toString()) + System.getProperty("line.separator");
        }
        /** Generates a detailed synopsis message showing all options and parameters. Follows the unix convention of
         * showing optional options and parameters in square brackets ({@code [ ]}).
         * @param optionSort comparator to sort options or {@code null} if options should not be sorted
         * @param clusterBooleanOptions {@code true} if boolean short options should be clustered into a single string
         * @return a detailed synopsis
         * @deprecated use {@link #detailedSynopsis(int, Comparator, boolean)} instead. */
        @Deprecated
        public String detailedSynopsis(final Comparator<Field> optionSort, final boolean clusterBooleanOptions) {
            return detailedSynopsis(0, optionSort, clusterBooleanOptions);
        }

        /** Generates a detailed synopsis message showing all options and parameters. Follows the unix convention of
         * showing optional options and parameters in square brackets ({@code [ ]}).
         * @param synopsisHeadingLength the length of the synopsis heading that will be displayed on the same line
         * @param optionSort comparator to sort options or {@code null} if options should not be sorted
         * @param clusterBooleanOptions {@code true} if boolean short options should be clustered into a single string
         * @return a detailed synopsis */
        public String detailedSynopsis(final int synopsisHeadingLength, final Comparator<Field> optionSort, final boolean clusterBooleanOptions) {
            Text optionText = ansi().new Text(0);
            final List<Field> fields = new ArrayList<>(optionFields); // iterate in declaration order
            if (optionSort != null) {
                Collections.sort(fields, optionSort);// iterate in specified sort order
            }
            if (clusterBooleanOptions) { // cluster all short boolean options into a single string
                final List<Field> booleanOptions = new ArrayList<>();
                final StringBuilder clusteredRequired = new StringBuilder("-");
                final StringBuilder clusteredOptional = new StringBuilder("-");
                for (final Field field : fields) {
                    if (field.getType() == boolean.class || field.getType() == Boolean.class) {
                        final Option option = field.getAnnotation(Option.class);
                        final String shortestName = ShortestFirst.sort(option.names())[0];
                        if (shortestName.length() == 2 && shortestName.startsWith("-")) {
                            booleanOptions.add(field);
                            if (option.required()) {
                                clusteredRequired.append(shortestName.substring(1));
                            } else {
                                clusteredOptional.append(shortestName.substring(1));
                            }
                        }
                    }
                }
                fields.removeAll(booleanOptions);
                if (clusteredRequired.length() > 1) { // initial length was 1
                    optionText = optionText.append(" ").append(colorScheme.optionText(clusteredRequired.toString()));
                }
                if (clusteredOptional.length() > 1) { // initial length was 1
                    optionText = optionText.append(" [").append(colorScheme.optionText(clusteredOptional.toString())).append("]");
                }
            }
            for (final Field field : fields) {
                final Option option = field.getAnnotation(Option.class);
                if (!option.hidden()) {
                    if (option.required()) {
                        optionText = appendOptionSynopsis(optionText, field, ShortestFirst.sort(option.names())[0], " ", "");
                        if (isMultiValue(field)) {
                            optionText = appendOptionSynopsis(optionText, field, ShortestFirst.sort(option.names())[0], " [", "]...");
                        }
                    } else {
                        optionText = appendOptionSynopsis(optionText, field, ShortestFirst.sort(option.names())[0], " [", "]");
                        if (isMultiValue(field)) {
                            optionText = optionText.append("...");
                        }
                    }
                }
            }
            for (final Field positionalParam : positionalParametersFields) {
                if (!positionalParam.getAnnotation(Parameters.class).hidden()) {
                    optionText = optionText.append(" ");
                    final Text label = parameterLabelRenderer.renderParameterLabel(positionalParam, colorScheme.ansi(), colorScheme.parameterStyles);
                    optionText = optionText.append(label);
                }
            }
            // Fix for #142: first line of synopsis overshoots max. characters
            final int firstColumnLength = commandName.length() + synopsisHeadingLength;

            // synopsis heading ("Usage: ") may be on the same line, so adjust column width
            final TextTable textTable = new TextTable(ansi(), firstColumnLength, usageHelpWidth - firstColumnLength);
            textTable.indentWrappedLines = 1; // don't worry about first line: options (2nd column) always start with a space

            // right-adjust the command name by length of synopsis heading
            final Text PADDING = Ansi.OFF.new Text(stringOf('X', synopsisHeadingLength));
            textTable.addRowValues(PADDING.append(colorScheme.commandText(commandName)), optionText);
            return textTable.toString().substring(synopsisHeadingLength); // cut off leading synopsis heading spaces
        }

        private Text appendOptionSynopsis(final Text optionText, final Field field, final String optionName, final String prefix, final String suffix) {
            final Text optionParamText = parameterLabelRenderer.renderParameterLabel(field, colorScheme.ansi(), colorScheme.optionParamStyles);
            return optionText.append(prefix)
                    .append(colorScheme.optionText(optionName))
                    .append(optionParamText)
                    .append(suffix);
        }

        /** Returns the number of characters the synopsis heading will take on the same line as the synopsis.
         * @return the number of characters the synopsis heading will take on the same line as the synopsis.
         * @see #detailedSynopsis(int, Comparator, boolean)
         */
        public int synopsisHeadingLength() {
            final String[] lines = Ansi.OFF.new Text(synopsisHeading).toString().split("\\r?\\n|\\r|%n", -1);
            return lines[lines.length - 1].length();
        }
        /**
         * <p>Returns a description of the {@linkplain Option options} supported by the application.
         * This implementation {@linkplain #createShortOptionNameComparator() sorts options alphabetically}, and shows
         * only the {@linkplain Option#hidden() non-hidden} options in a {@linkplain TextTable tabular format}
         * using the {@linkplain #createDefaultOptionRenderer() default renderer} and {@linkplain Layout default layout}.</p>
         * @return the fully formatted option list
         * @see #optionList(Layout, Comparator, IParamLabelRenderer)
         */
        public String optionList() {
            final Comparator<Field> sortOrder = sortOptions == null || sortOptions.booleanValue()
                    ? createShortOptionNameComparator()
                    : null;
            return optionList(createDefaultLayout(), sortOrder, parameterLabelRenderer);
        }

        /** Sorts all {@code Options} with the specified {@code comparator} (if the comparator is non-{@code null}),
         * then {@linkplain Layout#addOption(Field, CommandLine.Help.IParamLabelRenderer) adds} all non-hidden options to the
         * specified TextTable and returns the result of TextTable.toString().
         * @param layout responsible for rendering the option list
         * @param optionSort determines in what order {@code Options} should be listed. Declared order if {@code null}
         * @param valueLabelRenderer used for options with a parameter
         * @return the fully formatted option list
         */
        public String optionList(final Layout layout, final Comparator<Field> optionSort, final IParamLabelRenderer valueLabelRenderer) {
            final List<Field> fields = new ArrayList<>(optionFields); // options are stored in order of declaration
            if (optionSort != null) {
                Collections.sort(fields, optionSort); // default: sort options ABC
            }
            layout.addOptions(fields, valueLabelRenderer);
            return layout.toString();
        }

        /**
         * Returns the section of the usage help message that lists the parameters with their descriptions.
         * @return the section of the usage help message that lists the parameters
         */
        public String parameterList() {
            return parameterList(createDefaultLayout(), parameterLabelRenderer);
        }
        /**
         * Returns the section of the usage help message that lists the parameters with their descriptions.
         * @param layout the layout to use
         * @param paramLabelRenderer for rendering parameter names
         * @return the section of the usage help message that lists the parameters
         */
        public String parameterList(final Layout layout, final IParamLabelRenderer paramLabelRenderer) {
            layout.addPositionalParameters(positionalParametersFields, paramLabelRenderer);
            return layout.toString();
        }

        private static String heading(final Ansi ansi, final String values, final Object... params) {
            final StringBuilder sb = join(ansi, new String[] {values}, new StringBuilder(), params);
            String result = sb.toString();
            result = result.endsWith(System.getProperty("line.separator"))
                    ? result.substring(0, result.length() - System.getProperty("line.separator").length()) : result;
            return result + new String(spaces(countTrailingSpaces(values)));
        }
        private static char[] spaces(final int length) { final char[] result = new char[length]; Arrays.fill(result, ' '); return result; }
        private static int countTrailingSpaces(final String str) {
            if (str == null) {return 0;}
            int trailingSpaces = 0;
            for (int i = str.length() - 1; i >= 0 && str.charAt(i) == ' '; i--) { trailingSpaces++; }
            return trailingSpaces;
        }

        /** Formats each of the specified values and appends it to the specified StringBuilder.
         * @param ansi whether the result should contain ANSI escape codes or not
         * @param values the values to format and append to the StringBuilder
         * @param sb the StringBuilder to collect the formatted strings
         * @param params the parameters to pass to the format method when formatting each value
         * @return the specified StringBuilder */
        public static StringBuilder join(final Ansi ansi, final String[] values, final StringBuilder sb, final Object... params) {
            if (values != null) {
                final TextTable table = new TextTable(ansi, usageHelpWidth);
                table.indentWrappedLines = 0;
                for (final String summaryLine : values) {
                    final Text[] lines = ansi.new Text(format(summaryLine, params)).splitLines();
                    for (final Text line : lines) {  table.addRowValues(line); }
                }
                table.toString(sb);
            }
            return sb;
        }
        private static String format(final String formatString,  final Object... params) {
            return formatString == null ? "" : String.format(formatString, params);
        }
        /** Returns command custom synopsis as a string. A custom synopsis can be zero or more lines, and can be
         * specified declaratively with the {@link Command#customSynopsis()} annotation attribute or programmatically
         * by setting the Help instance's {@link Help#customSynopsis} field.
         * @param params Arguments referenced by the format specifiers in the synopsis strings
         * @return the custom synopsis lines combined into a single String (which may be empty)
         */
        public String customSynopsis(final Object... params) {
            return join(ansi(), customSynopsis, new StringBuilder(), params).toString();
        }
        /** Returns command description text as a string. Description text can be zero or more lines, and can be specified
         * declaratively with the {@link Command#description()} annotation attribute or programmatically by
         * setting the Help instance's {@link Help#description} field.
         * @param params Arguments referenced by the format specifiers in the description strings
         * @return the description lines combined into a single String (which may be empty)
         */
        public String description(final Object... params) {
            return join(ansi(), description, new StringBuilder(), params).toString();
        }
        /** Returns the command header text as a string. Header text can be zero or more lines, and can be specified
         * declaratively with the {@link Command#header()} annotation attribute or programmatically by
         * setting the Help instance's {@link Help#header} field.
         * @param params Arguments referenced by the format specifiers in the header strings
         * @return the header lines combined into a single String (which may be empty)
         */
        public String header(final Object... params) {
            return join(ansi(), header, new StringBuilder(), params).toString();
        }
        /** Returns command footer text as a string. Footer text can be zero or more lines, and can be specified
         * declaratively with the {@link Command#footer()} annotation attribute or programmatically by
         * setting the Help instance's {@link Help#footer} field.
         * @param params Arguments referenced by the format specifiers in the footer strings
         * @return the footer lines combined into a single String (which may be empty)
         */
        public String footer(final Object... params) {
            return join(ansi(), footer, new StringBuilder(), params).toString();
        }

        /** Returns the text displayed before the header text; the result of {@code String.format(headerHeading, params)}.
         * @param params the parameters to use to format the header heading
         * @return the formatted header heading */
        public String headerHeading(final Object... params) {
            return heading(ansi(), headerHeading, params);
        }

        /** Returns the text displayed before the synopsis text; the result of {@code String.format(synopsisHeading, params)}.
         * @param params the parameters to use to format the synopsis heading
         * @return the formatted synopsis heading */
        public String synopsisHeading(final Object... params) {
            return heading(ansi(), synopsisHeading, params);
        }

        /** Returns the text displayed before the description text; an empty string if there is no description,
         * otherwise the result of {@code String.format(descriptionHeading, params)}.
         * @param params the parameters to use to format the description heading
         * @return the formatted description heading */
        public String descriptionHeading(final Object... params) {
            return empty(descriptionHeading) ? "" : heading(ansi(), descriptionHeading, params);
        }

        /** Returns the text displayed before the positional parameter list; an empty string if there are no positional
         * parameters, otherwise the result of {@code String.format(parameterListHeading, params)}.
         * @param params the parameters to use to format the parameter list heading
         * @return the formatted parameter list heading */
        public String parameterListHeading(final Object... params) {
            return positionalParametersFields.isEmpty() ? "" : heading(ansi(), parameterListHeading, params);
        }

        /** Returns the text displayed before the option list; an empty string if there are no options,
         * otherwise the result of {@code String.format(optionListHeading, params)}.
         * @param params the parameters to use to format the option list heading
         * @return the formatted option list heading */
        public String optionListHeading(final Object... params) {
            return optionFields.isEmpty() ? "" : heading(ansi(), optionListHeading, params);
        }

        /** Returns the text displayed before the command list; an empty string if there are no commands,
         * otherwise the result of {@code String.format(commandListHeading, params)}.
         * @param params the parameters to use to format the command list heading
         * @return the formatted command list heading */
        public String commandListHeading(final Object... params) {
            return commands.isEmpty() ? "" : heading(ansi(), commandListHeading, params);
        }

        /** Returns the text displayed before the footer text; the result of {@code String.format(footerHeading, params)}.
         * @param params the parameters to use to format the footer heading
         * @return the formatted footer heading */
        public String footerHeading(final Object... params) {
            return heading(ansi(), footerHeading, params);
        }
        /** Returns a 2-column list with command names and the first line of their header or (if absent) description.
         * @return a usage help section describing the added commands */
        public String commandList() {
            if (commands.isEmpty()) { return ""; }
            final int commandLength = maxLength(commands.keySet());
            final Help.TextTable textTable = new Help.TextTable(ansi(),
                    new Help.Column(commandLength + 2, 2, Help.Column.Overflow.SPAN),
                    new Help.Column(usageHelpWidth - (commandLength + 2), 2, Help.Column.Overflow.WRAP));

            for (final Map.Entry<String, Help> entry : commands.entrySet()) {
                final Help command = entry.getValue();
                final String header = command.header != null && command.header.length > 0 ? command.header[0]
                        : (command.description != null && command.description.length > 0 ? command.description[0] : "");
                textTable.addRowValues(colorScheme.commandText(entry.getKey()), ansi().new Text(header));
            }
            return textTable.toString();
        }
        private static int maxLength(final Collection<String> any) {
            final List<String> strings = new ArrayList<>(any);
            Collections.sort(strings, Collections.reverseOrder(Help.shortestFirst()));
            return strings.get(0).length();
        }
        private static String join(final String[] names, final int offset, final int length, final String separator) {
            if (names == null) { return ""; }
            final StringBuilder result = new StringBuilder();
            for (int i = offset; i < offset + length; i++) {
                result.append((i > offset) ? separator : "").append(names[i]);
            }
            return result.toString();
        }
        private static String stringOf(final char chr, final int length) {
            final char[] buff = new char[length];
            Arrays.fill(buff, chr);
            return new String(buff);
        }

        /** Returns a {@code Layout} instance configured with the user preferences captured in this Help instance.
         * @return a Layout */
        public Layout createDefaultLayout() {
            return new Layout(colorScheme, new TextTable(colorScheme.ansi()), createDefaultOptionRenderer(), createDefaultParameterRenderer());
        }
        /** Returns a new default OptionRenderer which converts {@link Option Options} to five columns of text to match
         *  the default {@linkplain TextTable TextTable} column layout. The first row of values looks like this:
         * <ol>
         * <li>the required option marker</li>
         * <li>2-character short option name (or empty string if no short option exists)</li>
         * <li>comma separator (only if both short option and long option exist, empty string otherwise)</li>
         * <li>comma-separated string with long option name(s)</li>
         * <li>first element of the {@link Option#description()} array</li>
         * </ol>
         * <p>Following this, there will be one row for each of the remaining elements of the {@link
         *   Option#description()} array, and these rows look like {@code {"", "", "", "", option.description()[i]}}.</p>
         * <p>If configured, this option renderer adds an additional row to display the default field value.</p>
         * @return a new default OptionRenderer
         */
        public IOptionRenderer createDefaultOptionRenderer() {
            final DefaultOptionRenderer result = new DefaultOptionRenderer();
            result.requiredMarker = String.valueOf(requiredOptionMarker);
            if (showDefaultValues != null && showDefaultValues.booleanValue()) {
                result.command = this.command;
            }
            return result;
        }
        /** Returns a new minimal OptionRenderer which converts {@link Option Options} to a single row with two columns
         * of text: an option name and a description. If multiple names or descriptions exist, the first value is used.
         * @return a new minimal OptionRenderer */
        public static IOptionRenderer createMinimalOptionRenderer() {
            return new MinimalOptionRenderer();
        }

        /** Returns a new default ParameterRenderer which converts {@link Parameters Parameters} to four columns of
         * text to match the default {@linkplain TextTable TextTable} column layout. The first row of values looks like this:
         * <ol>
         * <li>empty string </li>
         * <li>empty string </li>
         * <li>parameter(s) label as rendered by the {@link IParamLabelRenderer}</li>
         * <li>first element of the {@link Parameters#description()} array</li>
         * </ol>
         * <p>Following this, there will be one row for each of the remaining elements of the {@link
         *   Parameters#description()} array, and these rows look like {@code {"", "", "", param.description()[i]}}.</p>
         * <p>If configured, this parameter renderer adds an additional row to display the default field value.</p>
         * @return a new default ParameterRenderer
         */
        public IParameterRenderer createDefaultParameterRenderer() {
            final DefaultParameterRenderer result = new DefaultParameterRenderer();
            result.requiredMarker = String.valueOf(requiredOptionMarker);
            return result;
        }
        /** Returns a new minimal ParameterRenderer which converts {@link Parameters Parameters} to a single row with
         * two columns of text: an option name and a description. If multiple descriptions exist, the first value is used.
         * @return a new minimal ParameterRenderer */
        public static IParameterRenderer createMinimalParameterRenderer() {
            return new MinimalParameterRenderer();
        }

        /** Returns a value renderer that returns the {@code paramLabel} if defined or the field name otherwise.
         * @return a new minimal ParamLabelRenderer */
        public static IParamLabelRenderer createMinimalParamLabelRenderer() {
            return new IParamLabelRenderer() {
                @Override
                public Text renderParameterLabel(final Field field, final Ansi ansi, final List<IStyle> styles) {
                    final String text = DefaultParamLabelRenderer.renderParameterName(field);
                    return ansi.apply(text, styles);
                }
                @Override
                public String separator() { return ""; }
            };
        }
        /** Returns a new default value renderer that separates option parameters from their {@linkplain Option
         * options} with the specified separator string, surrounds optional parameters with {@code '['} and {@code ']'}
         * characters and uses ellipses ("...") to indicate that any number of a parameter are allowed.
         * @return a new default ParamLabelRenderer
         */
        public IParamLabelRenderer createDefaultParamLabelRenderer() {
            return new DefaultParamLabelRenderer(separator);
        }
        /** Sorts Fields annotated with {@code Option} by their option name in case-insensitive alphabetic order. If an
         * Option has multiple names, the shortest name is used for the sorting. Help options follow non-help options.
         * @return a comparator that sorts fields by their option name in case-insensitive alphabetic order */
        public static Comparator<Field> createShortOptionNameComparator() {
            return new SortByShortestOptionNameAlphabetically();
        }
        /** Sorts Fields annotated with {@code Option} by their option {@linkplain Range#max max arity} first, by
         * {@linkplain Range#min min arity} next, and by {@linkplain #createShortOptionNameComparator() option name} last.
         * @return a comparator that sorts fields by arity first, then their option name */
        public static Comparator<Field> createShortOptionArityAndNameComparator() {
            return new SortByOptionArityAndNameAlphabetically();
        }
        /** Sorts short strings before longer strings.
         * @return a comparators that sorts short strings before longer strings */
        public static Comparator<String> shortestFirst() {
            return new ShortestFirst();
        }

        /** Returns whether ANSI escape codes are enabled or not.
         * @return whether ANSI escape codes are enabled or not
         */
        public Ansi ansi() {
            return colorScheme.ansi;
        }

        /** When customizing online help for {@link Option Option} details, a custom {@code IOptionRenderer} can be
         * used to create textual representation of an Option in a tabular format: one or more rows, each containing
         * one or more columns. The {@link Layout Layout} is responsible for placing these text values in the
         * {@link TextTable TextTable}. */
        public interface IOptionRenderer {
            /**
             * Returns a text representation of the specified Option and the Field that captures the option value.
             * @param option the command line option to show online usage help for
             * @param field the field that will hold the value for the command line option
             * @param parameterLabelRenderer responsible for rendering option parameters to text
             * @param scheme color scheme for applying ansi color styles to options and option parameters
             * @return a 2-dimensional array of text values: one or more rows, each containing one or more columns
             */
            Text[][] render(Option option, Field field, IParamLabelRenderer parameterLabelRenderer, ColorScheme scheme);
        }
        /** The DefaultOptionRenderer converts {@link Option Options} to five columns of text to match the default
         * {@linkplain TextTable TextTable} column layout. The first row of values looks like this:
         * <ol>
         * <li>the required option marker (if the option is required)</li>
         * <li>2-character short option name (or empty string if no short option exists)</li>
         * <li>comma separator (only if both short option and long option exist, empty string otherwise)</li>
         * <li>comma-separated string with long option name(s)</li>
         * <li>first element of the {@link Option#description()} array</li>
         * </ol>
         * <p>Following this, there will be one row for each of the remaining elements of the {@link
         *   Option#description()} array, and these rows look like {@code {"", "", "", option.description()[i]}}.</p>
         */
        static class DefaultOptionRenderer implements IOptionRenderer {
            public String requiredMarker = " ";
            public Object command;
            private String sep;
            private boolean showDefault;
            @Override
            public Text[][] render(final Option option, final Field field, final IParamLabelRenderer paramLabelRenderer, final ColorScheme scheme) {
                final String[] names = ShortestFirst.sort(option.names());
                final int shortOptionCount = names[0].length() == 2 ? 1 : 0;
                final String shortOption = shortOptionCount > 0 ? names[0] : "";
                sep = shortOptionCount > 0 && names.length > 1 ? "," : "";

                final String longOption = join(names, shortOptionCount, names.length - shortOptionCount, ", ");
                final Text longOptionText = createLongOptionText(field, paramLabelRenderer, scheme, longOption);

                showDefault = command != null && !option.help() && !isBoolean(field.getType());
                final Object defaultValue = createDefaultValue(field);

                final String requiredOption = option.required() ? requiredMarker : "";
                return renderDescriptionLines(option, scheme, requiredOption, shortOption, longOptionText, defaultValue);
            }

            private Object createDefaultValue(final Field field) {
                Object defaultValue = null;
                try {
                    defaultValue = field.get(command);
                    if (defaultValue == null) { showDefault = false; } // #201 don't show null default values
                    else if (field.getType().isArray()) {
                        final StringBuilder sb = new StringBuilder();
                        for (int i = 0; i < Array.getLength(defaultValue); i++) {
                            sb.append(i > 0 ? ", " : "").append(Array.get(defaultValue, i));
                        }
                        defaultValue = sb.insert(0, "[").append("]").toString();
                    }
                } catch (final Exception ex) {
                    showDefault = false;
                }
                return defaultValue;
            }

            private Text createLongOptionText(final Field field, final IParamLabelRenderer renderer, final ColorScheme scheme, final String longOption) {
                Text paramLabelText = renderer.renderParameterLabel(field, scheme.ansi(), scheme.optionParamStyles);

                // if no long option, fill in the space between the short option name and the param label value
                if (paramLabelText.length > 0 && longOption.length() == 0) {
                    sep = renderer.separator();
                    // #181 paramLabelText may be =LABEL or [=LABEL...]
                    final int sepStart = paramLabelText.plainString().indexOf(sep);
                    final Text prefix = paramLabelText.substring(0, sepStart);
                    paramLabelText = prefix.append(paramLabelText.substring(sepStart + sep.length()));
                }
                Text longOptionText = scheme.optionText(longOption);
                longOptionText = longOptionText.append(paramLabelText);
                return longOptionText;
            }

            private Text[][] renderDescriptionLines(final Option option,
                                                    final ColorScheme scheme,
                                                    final String requiredOption,
                                                    final String shortOption,
                                                    final Text longOptionText,
                                                    final Object defaultValue) {
                final Text EMPTY = Ansi.EMPTY_TEXT;
                final List<Text[]> result = new ArrayList<>();
                Text[] descriptionFirstLines = scheme.ansi().new Text(str(option.description(), 0)).splitLines();
                if (descriptionFirstLines.length == 0) {
                    if (showDefault) {
                        descriptionFirstLines = new Text[]{scheme.ansi().new Text("  Default: " + defaultValue)};
                        showDefault = false; // don't show the default value twice
                    } else {
                        descriptionFirstLines = new Text[]{ EMPTY };
                    }
                }
                result.add(new Text[] { scheme.optionText(requiredOption), scheme.optionText(shortOption),
                        scheme.ansi().new Text(sep), longOptionText, descriptionFirstLines[0] });
                for (int i = 1; i < descriptionFirstLines.length; i++) {
                    result.add(new Text[] { EMPTY, EMPTY, EMPTY, EMPTY, descriptionFirstLines[i] });
                }
                for (int i = 1; i < option.description().length; i++) {
                    final Text[] descriptionNextLines = scheme.ansi().new Text(option.description()[i]).splitLines();
                    for (final Text line : descriptionNextLines) {
                        result.add(new Text[] { EMPTY, EMPTY, EMPTY, EMPTY, line });
                    }
                }
                if (showDefault) {
                    result.add(new Text[] { EMPTY, EMPTY, EMPTY, EMPTY, scheme.ansi().new Text("  Default: " + defaultValue) });
                }
                return result.toArray(new Text[result.size()][]);
            }
        }
        /** The MinimalOptionRenderer converts {@link Option Options} to a single row with two columns of text: an
         * option name and a description. If multiple names or description lines exist, the first value is used. */
        static class MinimalOptionRenderer implements IOptionRenderer {
            @Override
            public Text[][] render(final Option option, final Field field, final IParamLabelRenderer parameterLabelRenderer, final ColorScheme scheme) {
                Text optionText = scheme.optionText(option.names()[0]);
                final Text paramLabelText = parameterLabelRenderer.renderParameterLabel(field, scheme.ansi(), scheme.optionParamStyles);
                optionText = optionText.append(paramLabelText);
                return new Text[][] {{ optionText,
                                        scheme.ansi().new Text(option.description().length == 0 ? "" : option.description()[0]) }};
            }
        }
        /** The MinimalParameterRenderer converts {@link Parameters Parameters} to a single row with two columns of
         * text: the parameters label and a description. If multiple description lines exist, the first value is used. */
        static class MinimalParameterRenderer implements IParameterRenderer {
            @Override
            public Text[][] render(final Parameters param, final Field field, final IParamLabelRenderer parameterLabelRenderer, final ColorScheme scheme) {
                return new Text[][] {{ parameterLabelRenderer.renderParameterLabel(field, scheme.ansi(), scheme.parameterStyles),
                        scheme.ansi().new Text(param.description().length == 0 ? "" : param.description()[0]) }};
            }
        }
        /** When customizing online help for {@link Parameters Parameters} details, a custom {@code IParameterRenderer}
         * can be used to create textual representation of a Parameters field in a tabular format: one or more rows,
         * each containing one or more columns. The {@link Layout Layout} is responsible for placing these text
         * values in the {@link TextTable TextTable}. */
        public interface IParameterRenderer {
            /**
             * Returns a text representation of the specified Parameters and the Field that captures the parameter values.
             * @param parameters the command line parameters to show online usage help for
             * @param field the field that will hold the value for the command line parameters
             * @param parameterLabelRenderer responsible for rendering parameter labels to text
             * @param scheme color scheme for applying ansi color styles to positional parameters
             * @return a 2-dimensional array of text values: one or more rows, each containing one or more columns
             */
            Text[][] render(Parameters parameters, Field field, IParamLabelRenderer parameterLabelRenderer, ColorScheme scheme);
        }
        /** The DefaultParameterRenderer converts {@link Parameters Parameters} to five columns of text to match the
         * default {@linkplain TextTable TextTable} column layout. The first row of values looks like this:
         * <ol>
         * <li>the required option marker (if the parameter's arity is to have at least one value)</li>
         * <li>empty string </li>
         * <li>empty string </li>
         * <li>parameter(s) label as rendered by the {@link IParamLabelRenderer}</li>
         * <li>first element of the {@link Parameters#description()} array</li>
         * </ol>
         * <p>Following this, there will be one row for each of the remaining elements of the {@link
         *   Parameters#description()} array, and these rows look like {@code {"", "", "", param.description()[i]}}.</p>
         */
        static class DefaultParameterRenderer implements IParameterRenderer {
            public String requiredMarker = " ";
            @Override
            public Text[][] render(final Parameters params, final Field field, final IParamLabelRenderer paramLabelRenderer, final ColorScheme scheme) {
                final Text label = paramLabelRenderer.renderParameterLabel(field, scheme.ansi(), scheme.parameterStyles);
                final Text requiredParameter = scheme.parameterText(Range.parameterArity(field).min > 0 ? requiredMarker : "");

                final Text EMPTY = Ansi.EMPTY_TEXT;
                final List<Text[]> result = new ArrayList<>();
                Text[] descriptionFirstLines = scheme.ansi().new Text(str(params.description(), 0)).splitLines();
                if (descriptionFirstLines.length == 0) { descriptionFirstLines = new Text[]{ EMPTY }; }
                result.add(new Text[] { requiredParameter, EMPTY, EMPTY, label, descriptionFirstLines[0] });
                for (int i = 1; i < descriptionFirstLines.length; i++) {
                    result.add(new Text[] { EMPTY, EMPTY, EMPTY, EMPTY, descriptionFirstLines[i] });
                }
                for (int i = 1; i < params.description().length; i++) {
                    final Text[] descriptionNextLines = scheme.ansi().new Text(params.description()[i]).splitLines();
                    for (final Text line : descriptionNextLines) {
                        result.add(new Text[] { EMPTY, EMPTY, EMPTY, EMPTY, line });
                    }
                }
                return result.toArray(new Text[result.size()][]);
            }
        }
        /** When customizing online usage help for an option parameter or a positional parameter, a custom
         * {@code IParamLabelRenderer} can be used to render the parameter name or label to a String. */
        public interface IParamLabelRenderer {

            /** Returns a text rendering of the Option parameter or positional parameter; returns an empty string
             * {@code ""} if the option is a boolean and does not take a parameter.
             * @param field the annotated field with a parameter label
             * @param ansi determines whether ANSI escape codes should be emitted or not
             * @param styles the styles to apply to the parameter label
             * @return a text rendering of the Option parameter or positional parameter */
            Text renderParameterLabel(Field field, Ansi ansi, List<IStyle> styles);

            /** Returns the separator between option name and param label.
             * @return the separator between option name and param label */
            String separator();
        }
        /**
         * DefaultParamLabelRenderer separates option parameters from their {@linkplain Option options} with a
         * {@linkplain DefaultParamLabelRenderer#separator separator} string, surrounds optional values
         * with {@code '['} and {@code ']'} characters and uses ellipses ("...") to indicate that any number of
         * values is allowed for options or parameters with variable arity.
         */
        static class DefaultParamLabelRenderer implements IParamLabelRenderer {
            /** The string to use to separate option parameters from their options. */
            public final String separator;
            /** Constructs a new DefaultParamLabelRenderer with the specified separator string. */
            public DefaultParamLabelRenderer(final String separator) {
                this.separator = Assert.notNull(separator, "separator");
            }
            @Override
            public String separator() { return separator; }
            @Override
            public Text renderParameterLabel(final Field field, final Ansi ansi, final List<IStyle> styles) {
                final boolean isOptionParameter = field.isAnnotationPresent(Option.class);
                final Range arity = isOptionParameter ? Range.optionArity(field) : Range.parameterCapacity(field);
                final String split = isOptionParameter ? field.getAnnotation(Option.class).split() : field.getAnnotation(Parameters.class).split();
                Text result = ansi.new Text("");
                String sep = isOptionParameter ? separator : "";
                Text paramName = ansi.apply(renderParameterName(field), styles);
                if (!empty(split)) { paramName = paramName.append("[" + split).append(paramName).append("]..."); } // #194
                for (int i = 0; i < arity.min; i++) {
                    result = result.append(sep).append(paramName);
                    sep = " ";
                }
                if (arity.isVariable) {
                    if (result.length == 0) { // arity="*" or arity="0..*"
                        result = result.append(sep + "[").append(paramName).append("]...");
                    } else if (!result.plainString().endsWith("...")) { // split param may already end with "..."
                        result = result.append("...");
                    }
                } else {
                    sep = result.length == 0 ? (isOptionParameter ? separator : "") : " ";
                    for (int i = arity.min; i < arity.max; i++) {
                        if (sep.trim().length() == 0) {
                            result = result.append(sep + "[").append(paramName);
                        } else {
                            result = result.append("[" + sep).append(paramName);
                        }
                        sep  = " ";
                    }
                    for (int i = arity.min; i < arity.max; i++) { result = result.append("]"); }
                }
                return result;
            }
            private static String renderParameterName(final Field field) {
                String result = null;
                if (field.isAnnotationPresent(Option.class)) {
                    result = field.getAnnotation(Option.class).paramLabel();
                } else if (field.isAnnotationPresent(Parameters.class)) {
                    result = field.getAnnotation(Parameters.class).paramLabel();
                }
                if (result != null && result.trim().length() > 0) {
                    return result.trim();
                }
                String name = field.getName();
                if (Map.class.isAssignableFrom(field.getType())) { // #195 better param labels for map fields
                    final Class<?>[] paramTypes = getTypeAttribute(field);
                    if (paramTypes.length < 2 || paramTypes[0] == null || paramTypes[1] == null) {
                        name = "String=String";
                    } else { name = paramTypes[0].getSimpleName() + "=" + paramTypes[1].getSimpleName(); }
                }
                return "<" + name + ">";
            }
        }
        /** Use a Layout to format usage help text for options and parameters in tabular format.
         * <p>Delegates to the renderers to create {@link Text} values for the annotated fields, and uses a
         * {@link TextTable} to display these values in tabular format. Layout is responsible for deciding which values
         * to display where in the table. By default, Layout shows one option or parameter per table row.</p>
         * <p>Customize by overriding the {@link #layout(Field, CommandLine.Help.Ansi.Text[][])} method.</p>
         * @see IOptionRenderer rendering options to text
         * @see IParameterRenderer rendering parameters to text
         * @see TextTable showing values in a tabular format
         */
        public static class Layout {
            protected final ColorScheme colorScheme;
            protected final TextTable table;
            protected IOptionRenderer optionRenderer;
            protected IParameterRenderer parameterRenderer;

            /** Constructs a Layout with the specified color scheme, a new default TextTable, the
             * {@linkplain Help#createDefaultOptionRenderer() default option renderer}, and the
             * {@linkplain Help#createDefaultParameterRenderer() default parameter renderer}.
             * @param colorScheme the color scheme to use for common, auto-generated parts of the usage help message */
            public Layout(final ColorScheme colorScheme) { this(colorScheme, new TextTable(colorScheme.ansi())); }

            /** Constructs a Layout with the specified color scheme, the specified TextTable, the
             * {@linkplain Help#createDefaultOptionRenderer() default option renderer}, and the
             * {@linkplain Help#createDefaultParameterRenderer() default parameter renderer}.
             * @param colorScheme the color scheme to use for common, auto-generated parts of the usage help message
             * @param textTable the TextTable to lay out parts of the usage help message in tabular format */
            public Layout(final ColorScheme colorScheme, final TextTable textTable) {
                this(colorScheme, textTable, new DefaultOptionRenderer(), new DefaultParameterRenderer());
            }
            /** Constructs a Layout with the specified color scheme, the specified TextTable, the
             * specified option renderer and the specified parameter renderer.
             * @param colorScheme the color scheme to use for common, auto-generated parts of the usage help message
             * @param optionRenderer the object responsible for rendering Options to Text
             * @param parameterRenderer the object responsible for rendering Parameters to Text
             * @param textTable the TextTable to lay out parts of the usage help message in tabular format */
            public Layout(final ColorScheme colorScheme, final TextTable textTable, final IOptionRenderer optionRenderer, final IParameterRenderer parameterRenderer) {
                this.colorScheme       = Assert.notNull(colorScheme, "colorScheme");
                this.table             = Assert.notNull(textTable, "textTable");
                this.optionRenderer    = Assert.notNull(optionRenderer, "optionRenderer");
                this.parameterRenderer = Assert.notNull(parameterRenderer, "parameterRenderer");
            }
            /**
             * Copies the specified text values into the correct cells in the {@link TextTable}. This implementation
             * delegates to {@link TextTable#addRowValues(CommandLine.Help.Ansi.Text...)} for each row of values.
             * <p>Subclasses may override.</p>
             * @param field the field annotated with the specified Option or Parameters
             * @param cellValues the text values representing the Option/Parameters, to be displayed in tabular form
             */
            public void layout(final Field field, final Text[][] cellValues) {
                for (final Text[] oneRow : cellValues) {
                    table.addRowValues(oneRow);
                }
            }
            /** Calls {@link #addOption(Field, CommandLine.Help.IParamLabelRenderer)} for all non-hidden Options in the list.
             * @param fields fields annotated with {@link Option} to add usage descriptions for
             * @param paramLabelRenderer object that knows how to render option parameters */
            public void addOptions(final List<Field> fields, final IParamLabelRenderer paramLabelRenderer) {
                for (final Field field : fields) {
                    final Option option = field.getAnnotation(Option.class);
                    if (!option.hidden()) {
                        addOption(field, paramLabelRenderer);
                    }
                }
            }
            /**
             * Delegates to the {@link #optionRenderer option renderer} of this layout to obtain
             * text values for the specified {@link Option}, and then calls the {@link #layout(Field, CommandLine.Help.Ansi.Text[][])}
             * method to write these text values into the correct cells in the TextTable.
             * @param field the field annotated with the specified Option
             * @param paramLabelRenderer knows how to render option parameters
             */
            public void addOption(final Field field, final IParamLabelRenderer paramLabelRenderer) {
                final Option option = field.getAnnotation(Option.class);
                final Text[][] values = optionRenderer.render(option, field, paramLabelRenderer, colorScheme);
                layout(field, values);
            }
            /** Calls {@link #addPositionalParameter(Field, CommandLine.Help.IParamLabelRenderer)} for all non-hidden Parameters in the list.
             * @param fields fields annotated with {@link Parameters} to add usage descriptions for
             * @param paramLabelRenderer knows how to render option parameters */
            public void addPositionalParameters(final List<Field> fields, final IParamLabelRenderer paramLabelRenderer) {
                for (final Field field : fields) {
                    final Parameters parameters = field.getAnnotation(Parameters.class);
                    if (!parameters.hidden()) {
                        addPositionalParameter(field, paramLabelRenderer);
                    }
                }
            }
            /**
             * Delegates to the {@link #parameterRenderer parameter renderer} of this layout
             * to obtain text values for the specified {@link Parameters}, and then calls
             * {@link #layout(Field, CommandLine.Help.Ansi.Text[][])} to write these text values into the correct cells in the TextTable.
             * @param field the field annotated with the specified Parameters
             * @param paramLabelRenderer knows how to render option parameters
             */
            public void addPositionalParameter(final Field field, final IParamLabelRenderer paramLabelRenderer) {
                final Parameters option = field.getAnnotation(Parameters.class);
                final Text[][] values = parameterRenderer.render(option, field, paramLabelRenderer, colorScheme);
                layout(field, values);
            }
            /** Returns the section of the usage help message accumulated in the TextTable owned by this layout. */
            @Override public String toString() {
                return table.toString();
            }
        }
        /** Sorts short strings before longer strings. */
        static class ShortestFirst implements Comparator<String> {
            @Override
            public int compare(final String o1, final String o2) {
                return o1.length() - o2.length();
            }
            /** Sorts the specified array of Strings shortest-first and returns it. */
            public static String[] sort(final String[] names) {
                Arrays.sort(names, new ShortestFirst());
                return names;
            }
        }
        /** Sorts {@code Option} instances by their name in case-insensitive alphabetic order. If an Option has
         * multiple names, the shortest name is used for the sorting. Help options follow non-help options. */
        static class SortByShortestOptionNameAlphabetically implements Comparator<Field> {
            @Override
            public int compare(final Field f1, final Field f2) {
                final Option o1 = f1.getAnnotation(Option.class);
                final Option o2 = f2.getAnnotation(Option.class);
                if (o1 == null) { return 1; } else if (o2 == null) { return -1; } // options before params
                final String[] names1 = ShortestFirst.sort(o1.names());
                final String[] names2 = ShortestFirst.sort(o2.names());
                int result = names1[0].toUpperCase().compareTo(names2[0].toUpperCase()); // case insensitive sort
                result = result == 0 ? -names1[0].compareTo(names2[0]) : result; // lower case before upper case
                return o1.help() == o2.help() ? result : o2.help() ? -1 : 1; // help options come last
            }
        }
        /** Sorts {@code Option} instances by their max arity first, then their min arity, then delegates to super class. */
        static class SortByOptionArityAndNameAlphabetically extends SortByShortestOptionNameAlphabetically {
            @Override
            public int compare(final Field f1, final Field f2) {
                final Option o1 = f1.getAnnotation(Option.class);
                final Option o2 = f2.getAnnotation(Option.class);
                final Range arity1 = Range.optionArity(f1);
                final Range arity2 = Range.optionArity(f2);
                int result = arity1.max - arity2.max;
                if (result == 0) {
                    result = arity1.min - arity2.min;
                }
                if (result == 0) { // arity is same
                    if (isMultiValue(f1) && !isMultiValue(f2)) { result = 1; } // f1 > f2
                    if (!isMultiValue(f1) && isMultiValue(f2)) { result = -1; } // f1 < f2
                }
                return result == 0 ? super.compare(f1, f2) : result;
            }
        }
        /**
         * <p>Responsible for spacing out {@link Text} values according to the {@link Column} definitions the table was
         * created with. Columns have a width, indentation, and an overflow policy that decides what to do if a value is
         * longer than the column's width.</p>
         */
        public static class TextTable {
            /**
             * Helper class to index positions in a {@code Help.TextTable}.
             * @since 2.0
             */
            public static class Cell {
                /** Table column index (zero based). */
                public final int column;
                /** Table row index (zero based). */
                public final int row;
                /** Constructs a new Cell with the specified coordinates in the table.
                 * @param column the zero-based table column
                 * @param row the zero-based table row */
                public Cell(final int column, final int row) { this.column = column; this.row = row; }
            }

            /** The column definitions of this table. */
            public final Column[] columns;

            /** The {@code char[]} slots of the {@code TextTable} to copy text values into. */
            protected final List<Text> columnValues = new ArrayList<>();

            /** By default, indent wrapped lines by 2 spaces. */
            public int indentWrappedLines = 2;

            private final Ansi ansi;

            /** Constructs a TextTable with five columns as follows:
             * <ol>
             * <li>required option/parameter marker (width: 2, indent: 0, TRUNCATE on overflow)</li>
             * <li>short option name (width: 2, indent: 0, TRUNCATE on overflow)</li>
             * <li>comma separator (width: 1, indent: 0, TRUNCATE on overflow)</li>
             * <li>long option name(s) (width: 24, indent: 1, SPAN multiple columns on overflow)</li>
             * <li>description line(s) (width: 51, indent: 1, WRAP to next row on overflow)</li>
             * </ol>
             * @param ansi whether to emit ANSI escape codes or not
             */
            public TextTable(final Ansi ansi) {
                // "* -c, --create                Creates a ...."
                this(ansi, new Column[] {
                            new Column(2,                                        0, TRUNCATE), // "*"
                            new Column(2,                                        0, TRUNCATE), // "-c"
                            new Column(1,                                        0, TRUNCATE), // ","
                            new Column(optionsColumnWidth - 2 - 2 - 1       , 1, SPAN),  // " --create"
                            new Column(usageHelpWidth - optionsColumnWidth, 1, WRAP) // " Creates a ..."
                    });
            }

            /** Constructs a new TextTable with columns with the specified width, all SPANning  multiple columns on
             * overflow except the last column which WRAPS to the next row.
             * @param ansi whether to emit ANSI escape codes or not
             * @param columnWidths the width of the table columns (all columns have zero indent)
             */
            public TextTable(final Ansi ansi, final int... columnWidths) {
                this.ansi = Assert.notNull(ansi, "ansi");
                columns = new Column[columnWidths.length];
                for (int i = 0; i < columnWidths.length; i++) {
                    columns[i] = new Column(columnWidths[i], 0, i == columnWidths.length - 1 ? SPAN: WRAP);
                }
            }
            /** Constructs a {@code TextTable} with the specified columns.
             * @param ansi whether to emit ANSI escape codes or not
             * @param columns columns to construct this TextTable with */
            public TextTable(final Ansi ansi, final Column... columns) {
                this.ansi = Assert.notNull(ansi, "ansi");
                this.columns = Assert.notNull(columns, "columns");
                if (columns.length == 0) { throw new IllegalArgumentException("At least one column is required"); }
            }
            /** Returns the {@code Text} slot at the specified row and column to write a text value into.
             * @param row the row of the cell whose Text to return
             * @param col the column of the cell whose Text to return
             * @return the Text object at the specified row and column
             * @since 2.0 */
            public Text textAt(final int row, final int col) { return columnValues.get(col + (row * columns.length)); }

            /** Returns the {@code Text} slot at the specified row and column to write a text value into.
             * @param row the row of the cell whose Text to return
             * @param col the column of the cell whose Text to return
             * @return the Text object at the specified row and column
             * @deprecated use {@link #textAt(int, int)} instead */
            @Deprecated
            public Text cellAt(final int row, final int col) { return textAt(row, col); }

            /** Returns the current number of rows of this {@code TextTable}.
             * @return the current number of rows in this TextTable */
            public int rowCount() { return columnValues.size() / columns.length; }

            /** Adds the required {@code char[]} slots for a new row to the {@link #columnValues} field. */
            public void addEmptyRow() {
                for (int i = 0; i < columns.length; i++) {
                    columnValues.add(ansi.new Text(columns[i].width));
                }
            }

            /** Delegates to {@link #addRowValues(CommandLine.Help.Ansi.Text...)}.
             * @param values the text values to display in each column of the current row */
            public void addRowValues(final String... values) {
                final Text[] array = new Text[values.length];
                for (int i = 0; i < array.length; i++) {
                    array[i] = values[i] == null ? Ansi.EMPTY_TEXT : ansi.new Text(values[i]);
                }
                addRowValues(array);
            }
            /**
             * Adds a new {@linkplain TextTable#addEmptyRow() empty row}, then calls {@link
             * TextTable#putValue(int, int, CommandLine.Help.Ansi.Text) putValue} for each of the specified values, adding more empty rows
             * if the return value indicates that the value spanned multiple columns or was wrapped to multiple rows.
             * @param values the values to write into a new row in this TextTable
             * @throws IllegalArgumentException if the number of values exceeds the number of Columns in this table
             */
            public void addRowValues(final Text... values) {
                if (values.length > columns.length) {
                    throw new IllegalArgumentException(values.length + " values don't fit in " +
                            columns.length + " columns");
                }
                addEmptyRow();
                for (int col = 0; col < values.length; col++) {
                    final int row = rowCount() - 1;// write to last row: previous value may have wrapped to next row
                    final Cell cell = putValue(row, col, values[col]);

                    // add row if a value spanned/wrapped and there are still remaining values
                    if ((cell.row != row || cell.column != col) && col != values.length - 1) {
                        addEmptyRow();
                    }
                }
            }
            /**
             * Writes the specified value into the cell at the specified row and column and returns the last row and
             * column written to. Depending on the Column's {@link Column#overflow Overflow} policy, the value may span
             * multiple columns or wrap to multiple rows when larger than the column width.
             * @param row the target row in the table
             * @param col the target column in the table to write to
             * @param value the value to write
             * @return a Cell indicating the position in the table that was last written to (since 2.0)
             * @throws IllegalArgumentException if the specified row exceeds the table's {@linkplain
             *          TextTable#rowCount() row count}
             * @since 2.0 (previous versions returned a {@code java.awt.Point} object)
             */
            public Cell putValue(int row, int col, Text value) {
                if (row > rowCount() - 1) {
                    throw new IllegalArgumentException("Cannot write to row " + row + ": rowCount=" + rowCount());
                }
                if (value == null || value.plain.length() == 0) { return new Cell(col, row); }
                final Column column = columns[col];
                int indent = column.indent;
                switch (column.overflow) {
                    case TRUNCATE:
                        copy(value, textAt(row, col), indent);
                        return new Cell(col, row);
                    case SPAN:
                        final int startColumn = col;
                        do {
                            final boolean lastColumn = col == columns.length - 1;
                            final int charsWritten = lastColumn
                                    ? copy(BreakIterator.getLineInstance(), value, textAt(row, col), indent)
                                    : copy(value, textAt(row, col), indent);
                            value = value.substring(charsWritten);
                            indent = 0;
                            if (value.length > 0) { // value did not fit in column
                                ++col;                // write remainder of value in next column
                            }
                            if (value.length > 0 && col >= columns.length) { // we filled up all columns on this row
                                addEmptyRow();
                                row++;
                                col = startColumn;
                                indent = column.indent + indentWrappedLines;
                            }
                        } while (value.length > 0);
                        return new Cell(col, row);
                    case WRAP:
                        final BreakIterator lineBreakIterator = BreakIterator.getLineInstance();
                        do {
                            final int charsWritten = copy(lineBreakIterator, value, textAt(row, col), indent);
                            value = value.substring(charsWritten);
                            indent = column.indent + indentWrappedLines;
                            if (value.length > 0) {  // value did not fit in column
                                ++row;                 // write remainder of value in next row
                                addEmptyRow();
                            }
                        } while (value.length > 0);
                        return new Cell(col, row);
                }
                throw new IllegalStateException(column.overflow.toString());
            }
            private static int length(final Text str) {
                return str.length; // TODO count some characters as double length
            }

            private int copy(final BreakIterator line, final Text text, final Text columnValue, final int offset) {
                // Deceive the BreakIterator to ensure no line breaks after '-' character
                line.setText(text.plainString().replace("-", "\u00ff"));
                int done = 0;
                for (int start = line.first(), end = line.next(); end != BreakIterator.DONE; start = end, end = line.next()) {
                    final Text word = text.substring(start, end); //.replace("\u00ff", "-"); // not needed
                    if (columnValue.maxLength >= offset + done + length(word)) {
                        done += copy(word, columnValue, offset + done); // TODO localized length
                    } else {
                        break;
                    }
                }
                if (done == 0 && length(text) > columnValue.maxLength) {
                    // The value is a single word that is too big to be written to the column. Write as much as we can.
                    done = copy(text, columnValue, offset);
                }
                return done;
            }
            private static int copy(final Text value, final Text destination, final int offset) {
                final int length = Math.min(value.length, destination.maxLength - offset);
                value.getStyledChars(value.from, length, destination, offset);
                return length;
            }

            /** Copies the text representation that we built up from the options into the specified StringBuilder.
             * @param text the StringBuilder to write into
             * @return the specified StringBuilder object (to allow method chaining and a more fluid API) */
            public StringBuilder toString(final StringBuilder text) {
                final int columnCount = this.columns.length;
                final StringBuilder row = new StringBuilder(usageHelpWidth);
                for (int i = 0; i < columnValues.size(); i++) {
                    final Text column = columnValues.get(i);
                    row.append(column.toString());
                    row.append(new String(spaces(columns[i % columnCount].width - column.length)));
                    if (i % columnCount == columnCount - 1) {
                        int lastChar = row.length() - 1;
                        while (lastChar >= 0 && row.charAt(lastChar) == ' ') {lastChar--;} // rtrim
                        row.setLength(lastChar + 1);
                        text.append(row.toString()).append(System.getProperty("line.separator"));
                        row.setLength(0);
                    }
                }
                //if (Ansi.enabled()) { text.append(Style.reset.off()); }
                return text;
            }
            @Override
            public String toString() { return toString(new StringBuilder()).toString(); }
        }
        /** Columns define the width, indent (leading number of spaces in a column before the value) and
         * {@linkplain Overflow Overflow} policy of a column in a {@linkplain TextTable TextTable}. */
        public static class Column {

            /** Policy for handling text that is longer than the column width:
             *  span multiple columns, wrap to the next row, or simply truncate the portion that doesn't fit. */
            public enum Overflow { TRUNCATE, SPAN, WRAP }

            /** Column width in characters */
            public final int width;

            /** Indent (number of empty spaces at the start of the column preceding the text value) */
            public final int indent;

            /** Policy that determines how to handle values larger than the column width. */
            public final Overflow overflow;
            public Column(final int width, final int indent, final Overflow overflow) {
                this.width = width;
                this.indent = indent;
                this.overflow = Assert.notNull(overflow, "overflow");
            }
        }

        /** All usage help message are generated with a color scheme that assigns certain styles and colors to common
         * parts of a usage message: the command name, options, positional parameters and option parameters.
         * Users may customize these styles by creating Help with a custom color scheme.
         * <p>Note that these options and styles may not be rendered if ANSI escape codes are not
         * {@linkplain Ansi#enabled() enabled}.</p>
         * @see Help#defaultColorScheme(Ansi)
         */
        public static class ColorScheme {
            public final List<IStyle> commandStyles = new ArrayList<>();
            public final List<IStyle> optionStyles = new ArrayList<>();
            public final List<IStyle> parameterStyles = new ArrayList<>();
            public final List<IStyle> optionParamStyles = new ArrayList<>();
            private final Ansi ansi;

            /** Constructs a new ColorScheme with {@link Help.Ansi#AUTO}. */
            public ColorScheme() { this(Ansi.AUTO); }

            /** Constructs a new ColorScheme with the specified Ansi enabled mode.
             * @param ansi whether to emit ANSI escape codes or not
             */
            public ColorScheme(final Ansi ansi) {this.ansi = Assert.notNull(ansi, "ansi"); }

            /** Adds the specified styles to the registered styles for commands in this color scheme and returns this color scheme.
             * @param styles the styles to add to the registered styles for commands in this color scheme
             * @return this color scheme to enable method chaining for a more fluent API */
            public ColorScheme commands(final IStyle... styles)     { return addAll(commandStyles, styles); }
            /** Adds the specified styles to the registered styles for options in this color scheme and returns this color scheme.
             * @param styles the styles to add to registered the styles for options in this color scheme
             * @return this color scheme to enable method chaining for a more fluent API */
            public ColorScheme options(final IStyle... styles)      { return addAll(optionStyles, styles);}
            /** Adds the specified styles to the registered styles for positional parameters in this color scheme and returns this color scheme.
             * @param styles the styles to add to registered the styles for parameters in this color scheme
             * @return this color scheme to enable method chaining for a more fluent API */
            public ColorScheme parameters(final IStyle... styles)   { return addAll(parameterStyles, styles);}
            /** Adds the specified styles to the registered styles for option parameters in this color scheme and returns this color scheme.
             * @param styles the styles to add to the registered styles for option parameters in this color scheme
             * @return this color scheme to enable method chaining for a more fluent API */
            public ColorScheme optionParams(final IStyle... styles) { return addAll(optionParamStyles, styles);}
            /** Returns a Text with all command styles applied to the specified command string.
             * @param command the command string to apply the registered command styles to
             * @return a Text with all command styles applied to the specified command string */
            public Ansi.Text commandText(final String command)         { return ansi().apply(command,     commandStyles); }
            /** Returns a Text with all option styles applied to the specified option string.
             * @param option the option string to apply the registered option styles to
             * @return a Text with all option styles applied to the specified option string */
            public Ansi.Text optionText(final String option)           { return ansi().apply(option,      optionStyles); }
            /** Returns a Text with all parameter styles applied to the specified parameter string.
             * @param parameter the parameter string to apply the registered parameter styles to
             * @return a Text with all parameter styles applied to the specified parameter string */
            public Ansi.Text parameterText(final String parameter)     { return ansi().apply(parameter,   parameterStyles); }
            /** Returns a Text with all optionParam styles applied to the specified optionParam string.
             * @param optionParam the option parameter string to apply the registered option parameter styles to
             * @return a Text with all option parameter styles applied to the specified option parameter string */
            public Ansi.Text optionParamText(final String optionParam) { return ansi().apply(optionParam, optionParamStyles); }

            /** Replaces colors and styles in this scheme with ones specified in system properties, and returns this scheme.
             * Supported property names:<ul>
             *     <li>{@code picocli.color.commands}</li>
             *     <li>{@code picocli.color.options}</li>
             *     <li>{@code picocli.color.parameters}</li>
             *     <li>{@code picocli.color.optionParams}</li>
             * </ul><p>Property values can be anything that {@link Help.Ansi.Style#parse(String)} can handle.</p>
             * @return this ColorScheme
             */
            public ColorScheme applySystemProperties() {
                replace(commandStyles,     System.getProperty("picocli.color.commands"));
                replace(optionStyles,      System.getProperty("picocli.color.options"));
                replace(parameterStyles,   System.getProperty("picocli.color.parameters"));
                replace(optionParamStyles, System.getProperty("picocli.color.optionParams"));
                return this;
            }
            private void replace(final List<IStyle> styles, final String property) {
                if (property != null) {
                    styles.clear();
                    addAll(styles, Style.parse(property));
                }
            }
            private ColorScheme addAll(final List<IStyle> styles, final IStyle... add) {
                styles.addAll(Arrays.asList(add));
                return this;
            }

            public Ansi ansi() {
                return ansi;
            }
        }

        /** Creates and returns a new {@link ColorScheme} initialized with picocli default values: commands are bold,
         *  options and parameters use a yellow foreground, and option parameters use italic.
         * @param ansi whether the usage help message should contain ANSI escape codes or not
         * @return a new default color scheme
         */
        public static ColorScheme defaultColorScheme(final Ansi ansi) {
            return new ColorScheme(ansi)
                    .commands(Style.bold)
                    .options(Style.fg_yellow)
                    .parameters(Style.fg_yellow)
                    .optionParams(Style.italic);
        }

        /** Provides methods and inner classes to support using ANSI escape codes in usage help messages. */
        public enum Ansi {
            /** Only emit ANSI escape codes if the platform supports it and system property {@code "picocli.ansi"}
             * is not set to any value other than {@code "true"} (case insensitive). */
            AUTO,
            /** Forced ON: always emit ANSI escape code regardless of the platform. */
            ON,
            /** Forced OFF: never emit ANSI escape code regardless of the platform. */
            OFF;
            static Text EMPTY_TEXT = OFF.new Text(0);
            static final boolean isWindows  = System.getProperty("os.name").startsWith("Windows");
            static final boolean isXterm    = System.getenv("TERM") != null && System.getenv("TERM").startsWith("xterm");
            static final boolean ISATTY = calcTTY();

            // http://stackoverflow.com/questions/1403772/how-can-i-check-if-a-java-programs-input-output-streams-are-connected-to-a-term
            static final boolean calcTTY() {
                if (isWindows && isXterm) { return true; } // Cygwin uses pseudo-tty and console is always null...
                try { return System.class.getDeclaredMethod("console").invoke(null) != null; }
                catch (final Throwable reflectionFailed) { return true; }
            }
            private static boolean ansiPossible() { return ISATTY && (!isWindows || isXterm); }

            /** Returns {@code true} if ANSI escape codes should be emitted, {@code false} otherwise.
             * @return ON: {@code true}, OFF: {@code false}, AUTO: if system property {@code "picocli.ansi"} is
             *      defined then return its boolean value, otherwise return whether the platform supports ANSI escape codes */
            public boolean enabled() {
                if (this == ON)  { return true; }
                if (this == OFF) { return false; }
                return (System.getProperty("picocli.ansi") == null ? ansiPossible() : Boolean.getBoolean("picocli.ansi"));
            }

            /** Defines the interface for an ANSI escape sequence. */
            public interface IStyle {

                /** The Control Sequence Introducer (CSI) escape sequence {@value}. */
                String CSI = "\u001B[";

                /** Returns the ANSI escape code for turning this style on.
                 * @return the ANSI escape code for turning this style on */
                String on();

                /** Returns the ANSI escape code for turning this style off.
                 * @return the ANSI escape code for turning this style off */
                String off();
            }

            /**
             * A set of pre-defined ANSI escape code styles and colors, and a set of convenience methods for parsing
             * text with embedded markup style names, as well as convenience methods for converting
             * styles to strings with embedded escape codes.
             */
            public enum Style implements IStyle {
                reset(0, 0), bold(1, 21), faint(2, 22), italic(3, 23), underline(4, 24), blink(5, 25), reverse(7, 27),
                fg_black(30, 39), fg_red(31, 39), fg_green(32, 39), fg_yellow(33, 39), fg_blue(34, 39), fg_magenta(35, 39), fg_cyan(36, 39), fg_white(37, 39),
                bg_black(40, 49), bg_red(41, 49), bg_green(42, 49), bg_yellow(43, 49), bg_blue(44, 49), bg_magenta(45, 49), bg_cyan(46, 49), bg_white(47, 49),
                ;
                private final int startCode;
                private final int endCode;

                Style(final int startCode, final int endCode) {this.startCode = startCode; this.endCode = endCode; }
                @Override
                public String on() { return CSI + startCode + "m"; }
                @Override
                public String off() { return CSI + endCode + "m"; }

                                /** Returns the concatenated ANSI escape codes for turning all specified styles on.
                 * @param styles the styles to generate ANSI escape codes for
                 * @return the concatenated ANSI escape codes for turning all specified styles on */
                public static String on(final IStyle... styles) {
                    final StringBuilder result = new StringBuilder();
                    for (final IStyle style : styles) {
                        result.append(style.on());
                    }
                    return result.toString();
                }
                                /** Returns the concatenated ANSI escape codes for turning all specified styles off.
                 * @param styles the styles to generate ANSI escape codes for
                 * @return the concatenated ANSI escape codes for turning all specified styles off */
                public static String off(final IStyle... styles) {
                    final StringBuilder result = new StringBuilder();
                    for (final IStyle style : styles) {
                        result.append(style.off());
                    }
                    return result.toString();
                }
                                /** Parses the specified style markup and returns the associated style.
                                 *  The markup may be one of the Style enum value names, or it may be one of the Style enum value
                                 *  names when {@code "fg_"} is prepended, or it may be one of the indexed colors in the 256 color palette.
                 * @param str the case-insensitive style markup to convert, e.g. {@code "blue"} or {@code "fg_blue"},
                 *          or {@code "46"} (indexed color) or {@code "0;5;0"} (RGB components of an indexed color)
                                 * @return the IStyle for the specified converter
                                 */
                public static IStyle fg(final String str) {
                    try { return Style.valueOf(str.toLowerCase(ENGLISH)); } catch (final Exception ignored) {}
                    try { return Style.valueOf("fg_" + str.toLowerCase(ENGLISH)); } catch (final Exception ignored) {}
                    return new Palette256Color(true, str);
                }
                                /** Parses the specified style markup and returns the associated style.
                                 *  The markup may be one of the Style enum value names, or it may be one of the Style enum value
                                 *  names when {@code "bg_"} is prepended, or it may be one of the indexed colors in the 256 color palette.
                                 * @param str the case-insensitive style markup to convert, e.g. {@code "blue"} or {@code "bg_blue"},
                 *          or {@code "46"} (indexed color) or {@code "0;5;0"} (RGB components of an indexed color)
                                 * @return the IStyle for the specified converter
                                 */
                public static IStyle bg(final String str) {
                    try { return Style.valueOf(str.toLowerCase(ENGLISH)); } catch (final Exception ignored) {}
                    try { return Style.valueOf("bg_" + str.toLowerCase(ENGLISH)); } catch (final Exception ignored) {}
                    return new Palette256Color(false, str);
                }
                /** Parses the specified comma-separated sequence of style descriptors and returns the associated
                 *  styles. For each markup, strings starting with {@code "bg("} are delegated to
                 *  {@link #bg(String)}, others are delegated to {@link #bg(String)}.
                 * @param commaSeparatedCodes one or more descriptors, e.g. {@code "bg(blue),underline,red"}
                 * @return an array with all styles for the specified descriptors
                 */
                public static IStyle[] parse(final String commaSeparatedCodes) {
                    final String[] codes = commaSeparatedCodes.split(",");
                    final IStyle[] styles = new IStyle[codes.length];
                    for(int i = 0; i < codes.length; ++i) {
                        if (codes[i].toLowerCase(ENGLISH).startsWith("fg(")) {
                            final int end = codes[i].indexOf(')');
                            styles[i] = Style.fg(codes[i].substring(3, end < 0 ? codes[i].length() : end));
                        } else if (codes[i].toLowerCase(ENGLISH).startsWith("bg(")) {
                            final int end = codes[i].indexOf(')');
                            styles[i] = Style.bg(codes[i].substring(3, end < 0 ? codes[i].length() : end));
                        } else {
                            styles[i] = Style.fg(codes[i]);
                        }
                    }
                    return styles;
                }
            }

            /** Defines a palette map of 216 colors: 6 * 6 * 6 cube (216 colors):
             * 16 + 36 * r + 6 * g + b (0 &lt;= r, g, b &lt;= 5). */
            static class Palette256Color implements IStyle {
                private final int fgbg;
                private final int color;

                Palette256Color(final boolean foreground, final String color) {
                    this.fgbg = foreground ? 38 : 48;
                    final String[] rgb = color.split(";");
                    if (rgb.length == 3) {
                        this.color = 16 + 36 * Integer.decode(rgb[0]) + 6 * Integer.decode(rgb[1]) + Integer.decode(rgb[2]);
                    } else {
                        this.color = Integer.decode(color);
                    }
                }
                @Override
                public String on() { return String.format(CSI + "%d;5;%dm", fgbg, color); }
                @Override
                public String off() { return CSI + (fgbg + 1) + "m"; }
            }
            private static class StyledSection {
                int startIndex, length;
                String startStyles, endStyles;
                StyledSection(final int start, final int len, final String style1, final String style2) {
                    startIndex = start; length = len; startStyles = style1; endStyles = style2;
                }
                StyledSection withStartIndex(final int newStart) {
                    return new StyledSection(newStart, length, startStyles, endStyles);
                }
            }

            /**
             * Returns a new Text object where all the specified styles are applied to the full length of the
             * specified plain text.
             * @param plainText the string to apply all styles to. Must not contain markup!
             * @param styles the styles to apply to the full plain text
             * @return a new Text object
             */
            public Text apply(final String plainText, final List<IStyle> styles) {
                if (plainText.length() == 0) { return new Text(0); }
                final Text result = new Text(plainText.length());
                final IStyle[] all = styles.toArray(new IStyle[styles.size()]);
                result.sections.add(new StyledSection(
                        0, plainText.length(), Style.on(all), Style.off(reverse(all)) + Style.reset.off()));
                result.plain.append(plainText);
                result.length = result.plain.length();
                return result;
            }

            private static <T> T[] reverse(final T[] all) {
                for (int i = 0; i < all.length / 2; i++) {
                    final T temp = all[i];
                    all[i] = all[all.length - i - 1];
                    all[all.length - i - 1] = temp;
                }
                return all;
            }
            /** Encapsulates rich text with styles and colors. Text objects may be constructed with Strings containing
             * markup like {@code @|bg(red),white,underline some text|@}, and this class converts the markup to ANSI
             * escape codes.
             * <p>
             * Internally keeps both an enriched and a plain text representation to allow layout components to calculate
             * text width while remaining unaware of the embedded ANSI escape codes.</p> */
            public class Text implements Cloneable {
                private final int maxLength;
                private int from;
                private int length;
                private StringBuilder plain = new StringBuilder();
                private List<StyledSection> sections = new ArrayList<>();

                /** Constructs a Text with the specified max length (for use in a TextTable Column).
                 * @param maxLength max length of this text */
                public Text(final int maxLength) { this.maxLength = maxLength; }

                /**
                 * Constructs a Text with the specified String, which may contain markup like
                 * {@code @|bg(red),white,underline some text|@}.
                 * @param input the string with markup to parse
                 */
                public Text(final String input) {
                    maxLength = -1;
                    plain.setLength(0);
                    int i = 0;

                    while (true) {
                        int j = input.indexOf("@|", i);
                        if (j == -1) {
                            if (i == 0) {
                                plain.append(input);
                                length = plain.length();
                                return;
                            }
                            plain.append(input.substring(i, input.length()));
                            length = plain.length();
                            return;
                        }
                        plain.append(input.substring(i, j));
                        final int k = input.indexOf("|@", j);
                        if (k == -1) {
                            plain.append(input);
                            length = plain.length();
                            return;
                        }

                        j += 2;
                        final String spec = input.substring(j, k);
                        final String[] items = spec.split(" ", 2);
                        if (items.length == 1) {
                            plain.append(input);
                            length = plain.length();
                            return;
                        }

                        final IStyle[] styles = Style.parse(items[0]);
                        addStyledSection(plain.length(), items[1].length(),
                                Style.on(styles), Style.off(reverse(styles)) + Style.reset.off());
                        plain.append(items[1]);
                        i = k + 2;
                    }
                }
                private void addStyledSection(final int start, final int length, final String startStyle, final String endStyle) {
                    sections.add(new StyledSection(start, length, startStyle, endStyle));
                }
                @Override
                public Object clone() {
                    try { return super.clone(); } catch (final CloneNotSupportedException e) { throw new IllegalStateException(e); }
                }

                public Text[] splitLines() {
                    final List<Text> result = new ArrayList<>();
                    boolean trailingEmptyString = false;
                    int start = 0, end = 0;
                    for (int i = 0; i < plain.length(); i++, end = i) {
                        final char c = plain.charAt(i);
                        boolean eol = c == '\n';
                        eol |= (c == '\r' && i + 1 < plain.length() && plain.charAt(i + 1) == '\n' && ++i > 0); // \r\n
                        eol |= c == '\r';
                        if (eol) {
                            result.add(this.substring(start, end));
                            trailingEmptyString = i == plain.length() - 1;
                            start = i + 1;
                        }
                    }
                    if (start < plain.length() || trailingEmptyString) {
                        result.add(this.substring(start, plain.length()));
                    }
                    return result.toArray(new Text[result.size()]);
                }

                /** Returns a new {@code Text} instance that is a substring of this Text. Does not modify this instance!
                 * @param start index in the plain text where to start the substring
                 * @return a new Text instance that is a substring of this Text */
                public Text substring(final int start) {
                    return substring(start, length);
                }

                /** Returns a new {@code Text} instance that is a substring of this Text. Does not modify this instance!
                 * @param start index in the plain text where to start the substring
                 * @param end index in the plain text where to end the substring
                 * @return a new Text instance that is a substring of this Text */
                public Text substring(final int start, final int end) {
                    final Text result = (Text) clone();
                    result.from = from + start;
                    result.length = end - start;
                    return result;
                }
                /** Returns a new {@code Text} instance with the specified text appended. Does not modify this instance!
                 * @param string the text to append
                 * @return a new Text instance */
                public Text append(final String string) {
                    return append(new Text(string));
                }

                /** Returns a new {@code Text} instance with the specified text appended. Does not modify this instance!
                 * @param other the text to append
                 * @return a new Text instance */
                public Text append(final Text other) {
                    final Text result = (Text) clone();
                    result.plain = new StringBuilder(plain.toString().substring(from, from + length));
                    result.from = 0;
                    result.sections = new ArrayList<>();
                    for (final StyledSection section : sections) {
                        result.sections.add(section.withStartIndex(section.startIndex - from));
                    }
                    result.plain.append(other.plain.toString().substring(other.from, other.from + other.length));
                    for (final StyledSection section : other.sections) {
                        final int index = result.length + section.startIndex - other.from;
                        result.sections.add(section.withStartIndex(index));
                    }
                    result.length = result.plain.length();
                    return result;
                }

                /**
                 * Copies the specified substring of this Text into the specified destination, preserving the markup.
                 * @param from start of the substring
                 * @param length length of the substring
                 * @param destination destination Text to modify
                 * @param offset indentation (padding)
                 */
                public void getStyledChars(final int from, final int length, final Text destination, final int offset) {
                    if (destination.length < offset) {
                        for (int i = destination.length; i < offset; i++) {
                            destination.plain.append(' ');
                        }
                        destination.length = offset;
                    }
                    for (final StyledSection section : sections) {
                        destination.sections.add(section.withStartIndex(section.startIndex - from + destination.length));
                    }
                    destination.plain.append(plain.toString().substring(from, from + length));
                    destination.length = destination.plain.length();
                }
                /** Returns the plain text without any formatting.
                 * @return the plain text without any formatting */
                public String plainString() {  return plain.toString().substring(from, from + length); }

                @Override
                public boolean equals(final Object obj) { return toString().equals(String.valueOf(obj)); }
                @Override
                public int hashCode() { return toString().hashCode(); }

                /** Returns a String representation of the text with ANSI escape codes embedded, unless ANSI is
                 * {@linkplain Ansi#enabled()} not enabled}, in which case the plain text is returned.
                 * @return a String representation of the text with ANSI escape codes embedded (if enabled) */
                @Override
                public String toString() {
                    if (!Ansi.this.enabled()) {
                        return plain.toString().substring(from, from + length);
                    }
                    if (length == 0) { return ""; }
                    final StringBuilder sb = new StringBuilder(plain.length() + 20 * sections.size());
                    StyledSection current = null;
                    final int end = Math.min(from + length, plain.length());
                    for (int i = from; i < end; i++) {
                        final StyledSection section = findSectionContaining(i);
                        if (section != current) {
                            if (current != null) { sb.append(current.endStyles); }
                            if (section != null) { sb.append(section.startStyles); }
                            current = section;
                        }
                        sb.append(plain.charAt(i));
                    }
                    if (current != null) { sb.append(current.endStyles); }
                    return sb.toString();
                }

                private StyledSection findSectionContaining(final int index) {
                    for (final StyledSection section : sections) {
                        if (index >= section.startIndex && index < section.startIndex + section.length) {
                            return section;
                        }
                    }
                    return null;
                }
            }
        }
    }

    /**
     * Utility class providing some defensive coding convenience methods.
     */
    private static final class Assert {
        /**
         * Throws a NullPointerException if the specified object is null.
         * @param object the object to verify
         * @param description error message
         * @param <T> type of the object to check
         * @return the verified object
         */
        static <T> T notNull(final T object, final String description) {
            if (object == null) {
                throw new NullPointerException(description);
            }
            return object;
        }
        private Assert() {} // private constructor: never instantiate
    }
    private enum TraceLevel { OFF, WARN, INFO, DEBUG;
        public boolean isEnabled(final TraceLevel other) { return ordinal() >= other.ordinal(); }
        private void print(final Tracer tracer, final String msg, final Object... params) {
            if (tracer.level.isEnabled(this)) { tracer.stream.printf(prefix(msg), params); }
        }
        private String prefix(final String msg) { return "[picocli " + this + "] " + msg; }
        static TraceLevel lookup(final String key) { return key == null ? WARN : empty(key) || "true".equalsIgnoreCase(key) ? INFO : valueOf(key); }
    }
    private static class Tracer {
        TraceLevel level = TraceLevel.lookup(System.getProperty("picocli.trace"));
        PrintStream stream = System.err;
        void warn (final String msg, final Object... params) { TraceLevel.WARN.print(this, msg, params); }
        void info (final String msg, final Object... params) { TraceLevel.INFO.print(this, msg, params); }
        void debug(final String msg, final Object... params) { TraceLevel.DEBUG.print(this, msg, params); }
        boolean isWarn()  { return level.isEnabled(TraceLevel.WARN); }
        boolean isInfo()  { return level.isEnabled(TraceLevel.INFO); }
        boolean isDebug() { return level.isEnabled(TraceLevel.DEBUG); }
    }
    /** Base class of all exceptions thrown by {@code picocli.CommandLine}.
     * @since 2.0 */
    public static class PicocliException extends RuntimeException {
        private static final long serialVersionUID = -2574128880125050818L;
        public PicocliException(final String msg) { super(msg); }
        public PicocliException(final String msg, final Exception ex) { super(msg, ex); }
    }
    /** Exception indicating a problem during {@code CommandLine} initialization.
     * @since 2.0 */
    public static class InitializationException extends PicocliException {
        private static final long serialVersionUID = 8423014001666638895L;
        public InitializationException(final String msg) { super(msg); }
        public InitializationException(final String msg, final Exception ex) { super(msg, ex); }
    }
    /** Exception indicating a problem while invoking a command or subcommand.
     * @since 2.0 */
    public static class ExecutionException extends PicocliException {
        private static final long serialVersionUID = 7764539594267007998L;
        private final CommandLine commandLine;
        public ExecutionException(final CommandLine commandLine, final String msg) {
            super(msg);
            this.commandLine = Assert.notNull(commandLine, "commandLine");
        }
        public ExecutionException(final CommandLine commandLine, final String msg, final Exception ex) {
            super(msg, ex);
            this.commandLine = Assert.notNull(commandLine, "commandLine");
        }
        /** Returns the {@code CommandLine} object for the (sub)command that could not be invoked.
         * @return the {@code CommandLine} object for the (sub)command where invocation failed.
         */
        public CommandLine getCommandLine() { return commandLine; }
    }

    /** Exception thrown by {@link ITypeConverter} implementations to indicate a String could not be converted. */
    public static class TypeConversionException extends PicocliException {
        private static final long serialVersionUID = 4251973913816346114L;
        public TypeConversionException(final String msg) { super(msg); }
    }
    /** Exception indicating something went wrong while parsing command line options. */
    public static class ParameterException extends PicocliException {
        private static final long serialVersionUID = 1477112829129763139L;
        private final CommandLine commandLine;

        /** Constructs a new ParameterException with the specified CommandLine and error message.
         * @param commandLine the command or subcommand whose input was invalid
         * @param msg describes the problem
         * @since 2.0 */
        public ParameterException(final CommandLine commandLine, final String msg) {
            super(msg);
            this.commandLine = Assert.notNull(commandLine, "commandLine");
        }
        /** Constructs a new ParameterException with the specified CommandLine and error message.
         * @param commandLine the command or subcommand whose input was invalid
         * @param msg describes the problem
         * @param ex the exception that caused this ParameterException
         * @since 2.0 */
        public ParameterException(final CommandLine commandLine, final String msg, final Exception ex) {
            super(msg, ex);
            this.commandLine = Assert.notNull(commandLine, "commandLine");
        }

        /** Returns the {@code CommandLine} object for the (sub)command whose input could not be parsed.
         * @return the {@code CommandLine} object for the (sub)command where parsing failed.
         * @since 2.0
         */
        public CommandLine getCommandLine() { return commandLine; }

        private static ParameterException create(final CommandLine cmd, final Exception ex, final String arg, final int i, final String[] args) {
            final String msg = ex.getClass().getSimpleName() + ": " + ex.getLocalizedMessage()
                    + " while processing argument at or before arg[" + i + "] '" + arg + "' in " + Arrays.toString(args) + ": " + ex.toString();
            return new ParameterException(cmd, msg, ex);
        }
    }
    /**
     * Exception indicating that a required parameter was not specified.
     */
    public static class MissingParameterException extends ParameterException {
        private static final long serialVersionUID = 5075678535706338753L;
        public MissingParameterException(final CommandLine commandLine, final String msg) {
            super(commandLine, msg);
        }

        private static MissingParameterException create(final CommandLine cmd, final Collection<Field> missing, final String separator) {
            if (missing.size() == 1) {
                return new MissingParameterException(cmd, "Missing required option '"
                        + describe(missing.iterator().next(), separator) + "'");
            }
            final List<String> names = new ArrayList<>(missing.size());
            for (final Field field : missing) {
                names.add(describe(field, separator));
            }
            return new MissingParameterException(cmd, "Missing required options " + names.toString());
        }
        private static String describe(final Field field, final String separator) {
            final String prefix = (field.isAnnotationPresent(Option.class))
                ? field.getAnnotation(Option.class).names()[0] + separator
                : "params[" + field.getAnnotation(Parameters.class).index() + "]" + separator;
            return prefix + Help.DefaultParamLabelRenderer.renderParameterName(field);
        }
    }

    /**
     * Exception indicating that multiple fields have been annotated with the same Option name.
     */
    public static class DuplicateOptionAnnotationsException extends InitializationException {
        private static final long serialVersionUID = -3355128012575075641L;
        public DuplicateOptionAnnotationsException(final String msg) { super(msg); }

        private static DuplicateOptionAnnotationsException create(final String name, final Field field1, final Field field2) {
            return new DuplicateOptionAnnotationsException("Option name '" + name + "' is used by both " +
                    field1.getDeclaringClass().getName() + "." + field1.getName() + " and " +
                    field2.getDeclaringClass().getName() + "." + field2.getName());
        }
    }
    /** Exception indicating that there was a gap in the indices of the fields annotated with {@link Parameters}. */
    public static class ParameterIndexGapException extends InitializationException {
        private static final long serialVersionUID = -1520981133257618319L;
        public ParameterIndexGapException(final String msg) { super(msg); }
    }
    /** Exception indicating that a command line argument could not be mapped to any of the fields annotated with
     * {@link Option} or {@link Parameters}. */
    public static class UnmatchedArgumentException extends ParameterException {
        private static final long serialVersionUID = -8700426380701452440L;
        public UnmatchedArgumentException(final CommandLine commandLine, final String msg) { super(commandLine, msg); }
        public UnmatchedArgumentException(final CommandLine commandLine, final Stack<String> args) { this(commandLine, new ArrayList<>(reverse(args))); }
        public UnmatchedArgumentException(final CommandLine commandLine, final List<String> args) { this(commandLine, "Unmatched argument" + (args.size() == 1 ? " " : "s ") + args); }
    }
    /** Exception indicating that more values were specified for an option or parameter than its {@link Option#arity() arity} allows. */
    public static class MaxValuesforFieldExceededException extends ParameterException {
        private static final long serialVersionUID = 6536145439570100641L;
        public MaxValuesforFieldExceededException(final CommandLine commandLine, final String msg) { super(commandLine, msg); }
    }
    /** Exception indicating that an option for a single-value option field has been specified multiple times on the command line. */
    public static class OverwrittenOptionException extends ParameterException {
        private static final long serialVersionUID = 1338029208271055776L;
        public OverwrittenOptionException(final CommandLine commandLine, final String msg) { super(commandLine, msg); }
    }
    /**
     * Exception indicating that an annotated field had a type for which no {@link ITypeConverter} was
     * {@linkplain #registerConverter(Class, ITypeConverter) registered}.
     */
    public static class MissingTypeConverterException extends ParameterException {
        private static final long serialVersionUID = -6050931703233083760L;
        public MissingTypeConverterException(final CommandLine commandLine, final String msg) { super(commandLine, msg); }
    }
}