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+== Tutorial
+
+=== Why OptionParser?
+
+When a Ruby program executes, it captures its command-line arguments
+and options into variable ARGV.
+This simple program just prints its \ARGV:
+
+  :include: argv.rb
+
+Execution, with arguments and options:
+
+  $ ruby argv.rb foo --bar --baz bat bam
+  ["foo", "--bar", "--baz", "bat", "bam"]
+
+The executing program is responsible for parsing and handling
+the command-line options.
+
+OptionParser offers methods for parsing and handling those options.
+
+With \OptionParser, you can define options so that for each option:
+
+- The code that defines the option and code that handles that option
+  are in the same place.
+- The option may take no argument, a required argument, or an optional argument.
+- The argument may be automatically converted to a specified class.
+- The argument may be restricted to specified _forms_.
+- The argument may be restricted to specified _values_.
+
+The class also has:
+
+- Method #summarize: returns a text summary of the options.
+- Method #help: displays automatically-generated help text.
+
+=== Defining Options
+
+A common way to define an option in \OptionParser
+is with instance method OptionParser#on.
+
+The method may be called with any number of arguments
+(whose order does not matter),
+and may also have a trailing optional keyword argument +into+.
+
+The given arguments determine the characteristics of the new option.
+These may include:
+
+- One or more short option names.
+- One or more long option names.
+- Whether the option takes no argument, an optional argument, or a required argument.
+- Acceptable _forms_ for the argument.
+- Acceptable _values_ for the argument.
+- A proc or method to be called when the parser encounters the option.
+- String descriptions for the option.
+
+=== Option Names
+
+You can give an option one or more names of two types:
+
+- Short (1-character) name, beginning with one hyphen (<tt>-</tt>).
+- Long (multi-character) name, beginning with two hyphens (<tt>--</tt>).
+
+==== Short Option Names
+
+A short option name consists of a hyphen and a single character.
+
+File +short_names.rb+
+defines an option with a short name, <tt>-x</tt>,
+and an option with two short names (aliases, in effect) <tt>-y</tt> and <tt>-z</tt>.
+
+  :include: short_names.rb
+
+Executions:
+
+  $ ruby short_names.rb -x
+  ["x", true]
+  $ ruby short_names.rb -1
+  ["-1 or -%", true]
+  $ ruby short_names.rb -%
+  ["-1 or -%", true]
+
+Multiple short names can "share" a hyphen:
+
+  $ ruby short_names.rb -x1%
+  ["x", true]
+  ["-1 or -%", true]
+  ["-1 or -%", true]
+
+This is a good time to note that giving an undefined option raises an exception:
+
+  $ ruby short_names.rb -z
+  short_names.rb:9:in `<main>': invalid option: -z (OptionParser::InvalidOption)
+
+==== Long Option Names
+
+A long option name consists of two hyphens and a one or more characters
+(usually two or more characters).
+
+File +long_names.rb+
+defines an option with a long name, <tt>--xxx</tt>,
+and an option with two long names (aliases, in effect) <tt>--y1%</tt> and <tt>--z2#</tt>.
+
+  :include: long_names.rb
+
+Executions:
+
+  $ ruby long_names.rb --xxx
+  ["-xxx", true]
+  $ ruby long_names.rb --y1%
+  ["--y1% or --z2#", true]
+  $ ruby long_names.rb --z2#
+  ["--y1% or --z2#", true]
+
+==== Mixing Option Names
+
+Many developers like to mix short and long option names,
+so that a short name is in effect an abbreviation of a long name.
+
+File +mixed_names.rb+
+defines options that each have both a short and a long name.
+
+  :include: mixed_names.rb
+
+Executions:
+
+  $ ruby mixed_names.rb -x
+  ["--xxx", true]
+  $ ruby mixed_names.rb --xxx
+  ["--xxx", true]
+  $ ruby mixed_names.rb -y
+  ["--y1%", true]
+  $ ruby mixed_names.rb --y1%
+  ["--y1%", true]
+
+=== Option Arguments
+
+An option may take no argument, a required argument, or an optional argument.
+
+==== Option with No Argument
+
+All the examples above define options with no argument.
+
+==== Option with Required Argument
+
+Specify a required argument for an option by adding a dummy word
+to its name definition.
+
+File +required_argument.rb+ defines two options;
+each has a required argument because the name definition has a following dummy word.
+
+  :include: required_argument.rb
+
+When an option is found, the given argument is yielded.
+
+Executions:
+
+  $ ruby required_argument.rb -x AAA
+  ["--xxx", "AAA"]
+  $ ruby required_argument.rb -y BBB
+  ["--yyy", "BBB"]
+
+Omitting a required argument raises an error:
+
+  $ ruby required_argument.rb -x
+  required_argument.rb:9:in `<main>': missing argument: -x (OptionParser::MissingArgument)
+
+==== Option with Optional Argument
+
+Specify an optional argument for an option by adding a dummy word
+enclosed in square brackets to its name definition.
+
+File +optional_argument.rb+ defines two options;
+each has an optional argument because the name definition has a following dummy word
+in square brackets.
+
+  :include: optional_argument.rb
+
+When an option with an argument is found, the given argument yielded.
+
+Executions:
+
+  $ ruby optional_argument.rb -x AAA
+  ["--xxx", "AAA"]
+  $ ruby optional_argument.rb -y BBB
+  ["--yyy", "BBB"]
+
+Omitting an optional argument does not raise an error.