ruby/doc/rdoc/markup_reference.rb

require 'rdoc'

# \Class \RDoc::MarkupReference exists only to provide a suitable home
# for a reference document for \RDoc markup.
#
# All objects defined in this class -- classes, modules, methods, aliases,
# attributes, and constants -- are solely for illustrating \RDoc markup,
# and have no other legitimate use.
#
# == About the Examples
#
# - Examples in this reference are Ruby code and comments;
#   certain differences from other sources
#   (such as C code and comments) are noted.
# - Almost all examples on this page are all RDoc-like;
#   that is, they have no explicit comment markers like Ruby <tt>#</tt>
#   or C <tt>/* ... */</tt>.
# - An example that shows rendered HTML output
#   displays that output in a blockquote:
#
#   >>>
#     Some stuff
#
# == \RDoc Sources
#
# The sources of \RDoc documentation vary according to the type of file:
#
# - <tt>.rb</tt> (Ruby code file):
#
#   - Markup may be found in Ruby comments:
#     A comment that immediately precedes the definition
#     of a Ruby class, module, method, alias, constant, or attribute
#     becomes the documentation for that defined object.
#   - An \RDoc directive may be found in:
#
#     - A trailing comment (on the same line as code);
#       see <tt>:nodoc:</tt>, <tt>:doc:</tt>, and <tt>:notnew:</tt>.
#     - A single-line comment;
#       see other {Directives}[rdoc-ref:RDoc::MarkupReference@Directives].
#
#   - Documentation may be derived from the Ruby code itself;
#     see {Documentation Derived from Ruby Code}[rdoc-ref:RDoc::MarkupReference@Documentation+Derived+from+Ruby+Code].
#
# - <tt>.c</tt> (C code file): markup is parsed from C comments.
#   A comment that immediately precedes
#   a function that implements a Ruby method,
#   or otherwise immediately precedes the definition of a Ruby object,
#   becomes the documentation for that object.
# - <tt>.rdoc</tt> (\RDoc markup text file) or <tt>.md</tt> (\RDoc markdown text file):
#   markup is parsed from the entire file.
#   The text is not associated with any code object,
#   but may (depending on how the documentation is built)
#   become a separate page.
#
# An <i>RDoc document</i>:
#
# - A (possibly multi-line) comment in a Ruby or C file
#   that generates \RDoc documentation (as above).
# - The entire markup (<tt>.rdoc</tt>) file or markdown (<tt>.md</tt>) file
#   (which is usually multi-line).
#
# === Blocks
#
# It's convenient to think of an \RDoc document as a sequence of _blocks_
# of various types (details at the links):
#
# - {Paragraph}[rdoc-ref:RDoc::MarkupReference@Paragraphs]:
#   an ordinary paragraph.
# - {Verbatim text block}[rdoc-ref:RDoc::MarkupReference@Verbatim+Text+Blocks]:
#   a block of text to be rendered literally.
# - {Code block}[rdoc-ref:RDoc::MarkupReference@Code+Blocks]:
#   a verbatim text block containing Ruby code,
#   to be rendered with code highlighting.
# - {Block quote}[rdoc-ref:RDoc::MarkupReference@Block+Quotes]:
#   a longish quoted passage, to be rendered with indentation
#   instead of quote marks.
# - {List}[rdoc-ref:RDoc::MarkupReference@Lists]: items for
#   a bullet list, numbered list, lettered list, or labeled list.
# - {Heading}[rdoc-ref:RDoc::MarkupReference@Headings]:
#   a heading.
# - {Horizontal rule}[rdoc-ref:RDoc::MarkupReference@Horizontal+Rules]:
#   a line across the rendered page.
# - {Directive}[rdoc-ref:RDoc::MarkupReference@Directives]:
#   various special directions for the rendering.
# - {Text Markup}[rdoc-ref:RDoc:MarkupReference@Text+Markup]:
#   text to be rendered in a special way.
#
# About the blocks:
#
# - Except for a paragraph, a block is distinguished by its indentation,
#   or by unusual initial or embedded characters.
# - Any block may appear independently
#   (that is, not nested in another block);
#   some blocks may be nested, as detailed below.
# - In a multi-line block,
#   \RDoc looks for the block's natural left margin,
#   which becomes the <em>base margin</em> for the block
#   and is the initial <em>current margin</em> for the block.
#
# ==== Paragraphs
#
# A paragraph consists of one or more non-empty lines of ordinary text,
# each beginning at the current margin.
#
# Note: Here, <em>ordinary text</em> means text that is <em>not identified</em>
# by indentation, or by unusual initial or embedded characters.
# See below.
#
# Paragraphs are separated by one or more empty lines.
#
# Example input:
#
#   \RDoc produces HTML and command-line documentation for Ruby projects.
#   \RDoc includes the rdoc and ri tools for generating and displaying
#   documentation from the command-line.
#
#   You'll love it.
#
# Rendered HTML:
# >>>
#   \RDoc produces HTML and command-line documentation for Ruby projects.
#   \RDoc includes the rdoc and ri tools for generating and displaying
#   documentation from the command-line.
#
#   You'll love it.
#
# A paragraph may contain nested blocks, including:
#
# - {Verbatim text blocks}[rdoc-ref:RDoc::MarkupReference@Verbatim+Text+Blocks].
# - {Code blocks}[rdoc-ref:RDoc::MarkupReference@Code+Blocks].
# - {Block quotes}[rdoc-ref:RDoc::MarkupReference@Block+Quotes].
# - {Lists}[rdoc-ref:RDoc::MarkupReference@Lists].
# - {Headings}[rdoc-ref:RDoc::MarkupReference@Headings].
# - {Horizontal rules}[rdoc-ref:RDoc::MarkupReference@Horizontal+Rules].
# - {Text Markup}[rdoc-ref:RDoc:MarkupReference@Text+Markup].
#
# ==== Verbatim Text Blocks
#
# Text indented farther than the current margin becomes a <em>verbatim text block</em>
# (or a code block, described next).
# In the rendered HTML, such text:
#
# - Is indented.
# - Has a contrasting background color.
#
# The verbatim text block ends at the first line beginning at the current margin.
#
# Example input:
#
#   This is not verbatim text.
#
#     This is verbatim text.
#       Whitespace is honored.     # See?
#         Whitespace is honored.     # See?
#
#     This is still the same verbatim text block.
#
#   This is not verbatim text.
#
# Rendered HTML:
# >>>
#   This is not verbatim text.
#
#     This is verbatim text.
#       Whitespace is honored.     # See?
#         Whitespace is honored.     # See?
#
#     This is still the same verbatim text block.
#
#   This is not verbatim text.
#
# A verbatim text block may not contain nested blocks of any kind
# -- it's verbatim.
#
# ==== Code Blocks
#
# A special case of verbatim text is the <em>code block</em>,
# which is merely verbatim text that \RDoc recognizes as Ruby code:
#
# In the rendered HTML, the code block:
#
# - Is indented.
# - Has a contrasting background color.
# - Has syntax highlighting.
#
# Example input:
#
#   Consider this method:
#
#     def foo(name = '', value = 0)
#       @name = name      # Whitespace is still honored.
#       @value = value
#     end
#
#
# Rendered HTML:
# >>>
#   Consider this method:
#
#     def foo(name = '', value = 0)
#       @name = name      # Whitespace is still honored.
#       @value = value
#     end
#
# Pro tip:  If your indented Ruby code does not get highlighted,
# it may contain a syntax error.
#
# A code block may not contain nested blocks of any kind
# -- it's verbatim.
#
# ==== Block Quotes
#
# You can use the characters <tt>>>></tt> (unindented),
# followed by indented text, to treat the text
# as a {block quote}[https://en.wikipedia.org/wiki/Block_quotation]:
#
# Example input:
#
#   Here's a block quote:
#   >>>
#     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer
#     commodo quam iaculis massa posuere, dictum fringilla justo pulvinar.
#     Quisque turpis erat, pharetra eu dui at, sollicitudin accumsan nulla.
#
#     Aenean congue ligula eu ligula molestie, eu pellentesque purus
#     faucibus. In id leo non ligula condimentum lobortis. Duis vestibulum,
#     diam in pellentesque aliquet, mi tellus placerat sapien, id euismod
#     purus magna ut tortor.
#
# Rendered HTML:
#
# >>>
#   Here's a block quote:
#   >>>
#     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer
#     commodo quam iaculis massa posuere, dictum fringilla justo pulvinar.
#     Quisque turpis erat, pharetra eu dui at, sollicitudin accumsan nulla.
#
#     Aenean congue ligula eu ligula molestie, eu pellentesque purus
#     faucibus. In id leo non ligula condimentum lobortis. Duis vestibulum,
#     diam in pellentesque aliquet, mi tellus placerat sapien, id euismod
#     purus magna ut tortor.
#
# Note that, unlike verbatim text, single newlines are not honored,
# but that a double newline begins a new paragraph in the block quote.
#
# A block quote may contain nested blocks, including:
#
# - Other block quotes.
# - {Paragraphs}[rdoc-ref:RDoc::MarkupReference@Paragraphs].
# - {Verbatim text blocks}[rdoc-ref:RDoc::MarkupReference@Verbatim+Text+Blocks].
# - {Code blocks}[rdoc-ref:RDoc::MarkupReference@Code+Blocks].
# - {Lists}[rdoc-ref:RDoc::MarkupReference@Lists].
# - {Headings}[rdoc-ref:RDoc::MarkupReference@Headings].
# - {Horizontal rules}[rdoc-ref:RDoc::MarkupReference@Horizontal+Rules].
# - {Text Markup}[rdoc-ref:RDoc:MarkupReference@Text+Markup].
#
# ==== Lists
#
# Each type of list item is marked by a special beginning:
#
# - Bullet list item: Begins with a hyphen or asterisk.
# - Numbered list item: Begins with digits and a period.
# - Lettered list item: Begins with an alphabetic character and a period.
# - Labeled list item: Begins with one of:
#   - Square-bracketed text.
#   - A word followed by two colons.
#
# A list begins with a list item and continues, even across blank lines,
# as long as list items of the same type are found at the same indentation level.
#
# A new list resets the current margin inward.
# Additional lines of text aligned at that margin
# are part of the continuing list item.
#
# A list item may be continued on additional lines that are aligned
# with the first line.  See examples below.
#
# A list item may contain nested blocks, including:
#
# - Other lists of any type.
# - {Paragraphs}[rdoc-ref:RDoc::MarkupReference@Paragraphs].
# - {Verbatim text blocks}[rdoc-ref:RDoc::MarkupReference@Verbatim+Text+Blocks].
# - {Code blocks}[rdoc-ref:RDoc::MarkupReference@Code+Blocks].
# - {Block quotes}[rdoc-ref:RDoc::MarkupReference@Block+Quotes].
# - {Headings}[rdoc-ref:RDoc::MarkupReference@Headings].
# - {Horizontal rules}[rdoc-ref:RDoc::MarkupReference@Horizontal+Rules].
# - {Text Markup}[rdoc-ref:RDoc:MarkupReference@Text+Markup].
#
# ===== Bullet Lists
#
# A bullet list item begins with a hyphen or asterisk.
#
# Example input:
#
#   - An item.
#   - Another.
#   - An item spanning
#     multiple lines.
#
#   * Yet another.
#   - Last one.
#
# Rendered HTML:
# >>>
#   - An item.
#   - Another.
#   - An item spanning
#     multiple lines.
#
#   * Yet another.
#   - Last one.
#
# ===== Numbered Lists
#
# A numbered list item begins with digits and a period.
#
# The items are automatically re-numbered.
#
# Example input:
#
#   100. An item.
#   10. Another.
#   1. An item spanning
#      multiple lines.
#
#   1. Yet another.
#   1000. Last one.
#
# Rendered HTML:
# >>>
#   100. An item.
#   10. Another.
#   1. An item spanning
#      multiple lines.
#
#   1. Yet another.
#   1000. Last one.
#
# ===== Lettered Lists
#
# A lettered list item begins with letters and a period.
#
# The items are automatically "re-lettered."
#
# Example input:
#
#   z. An item.
#   y. Another.
#   x. An item spanning
#      multiple lines.
#
#   x. Yet another.
#   a. Last one.
#
# Rendered HTML:
# >>>
#   z. An item.
#   y. Another.
#
#   x. Yet another.
#   a. Last one.
#
# ===== Labeled Lists
#
# A labeled list item begins with one of:
#
# - Square-bracketed text: the label and text are on two lines.
# - A word followed by two colons: the label and text are on the same line.
#
# Example input:
#
#   [foo] An item.
#   bat:: Another.
#   [bag] An item spanning
#         multiple lines.
#
#   [bar baz] Yet another.
#   bam:: Last one.
#
# Rendered HTML:
# >>>
#   [foo] An item.
#   bat:: Another.
#   [bag] An item spanning
#         multiple lines.
#
#   [bar baz] Yet another.
#   bam:: Last one.
#
# ==== Headings
#
# A heading begins with up to six equal-signs, followed by heading text.
# Whitespace between those and the heading text is optional.
#
# Examples:
#
#   = Section 1
#   == Section 1.1
#   === Section 1.1.1
#   === Section 1.1.2
#   == Section 1.2
#   = Section 2
#   = Foo
#   == Bar
#   === Baz
#   ==== Bam
#   ===== Bat
#   ====== Bad
#   ============Still a Heading (Level 6)
#   \== Not a Heading
#
# A heading may contain only one type of nested block:
#
# - {Text Markup}[rdoc-ref:RDoc:MarkupReference@Text+Markup].
#
# ==== Horizontal Rules
#
# A horizontal rule consists of a line with three or more hyphens
# and nothing more.
#
# Example input:
#
#   ---
#   --- Not a horizontal rule.
#
#   -- Also not a horizontal rule.
#   ---
#
# Rendered HTML:
# >>>
#   ---
#   --- Not a horizontal rule.
#
#   -- Also not a horizontal rule.
#   ---
#
# ==== Directives
#
# ===== Directives for Allowing or Suppressing Documentation
#
# - <tt># :stopdoc:</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that \RDoc should ignore markup
#     until next <tt>:startdoc:</tt> directive or end-of-file.
#
# - <tt># :startdoc:</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that \RDoc should resume parsing markup.
#
# - <tt># :enddoc:</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that \RDoc should ignore markup to end-of-file
#     regardless of other directives.
#
# - <tt># :nodoc:</tt>:
#
#   - Appended to a line of code
#     that defines a class, module, method, alias, constant, or attribute.
#
#   - Specifies that the defined object should not be documented.
#
#   - For a method definition in C code, it the directive must be in the comment line
#     immediately preceding the definition:
#
#         /* :nodoc: */
#         static VALUE
#         some_method(VALUE self)
#         {
#             return self;
#         }
#
#     Note that this directive has <em>no effect at all</em>
#     when placed at the method declaration:
#
#         /* :nodoc: */
#         rb_define_method(cMyClass, "do_something", something_func, 0);
#
#     The above comment is just a comment and has nothing to do with \RDoc.
#     Therefore, +do_something+ method will be reported as "undocumented"
#     unless that method or function is documented elsewhere.
#
#   - For a constant definition in C code, this directive <em>can not work</em>
#     because there is no "implementation" place for a constant.
#
# - <tt># :nodoc: all</tt>:
#
#   - Appended to a line of code
#     that defines a class or module.
#   - Specifies that the class or module should not be documented.
#     By default, however, a nested class or module _will_ be documented.
#
# - <tt># :doc:</tt>:
#
#   - Appended to a line of code
#     that defines a class, module, method, alias, constant, or attribute.
#   - Specifies the defined object should be documented, even if it otherwise
#     would not be documented.
#
# - <tt># :notnew:</tt> (aliased as <tt>:not_new:</tt> and <tt>:not-new:</tt>):
#
#   - Appended to a line of code
#     that defines instance method +initialize+.
#   - Specifies that singleton method +new+ should not be documented.
#     By default, Ruby fakes a corresponding singleton method +new+,
#     which \RDoc includes in the documentation.
#     Note that instance method +initialize+ is private, and so by default
#     is not documented.
#
# For Ruby code, but not for other \RDoc sources,
# there is a shorthand for <tt>:stopdoc:</tt> and <tt>:startdoc:</tt>:
#
#   # Documented.
#   #--
#   # Not documented.
#   #++
#   # Documented.
#
# For C code, any of directives <tt>:startdoc:</tt>, <tt>:stopdoc:</tt>,
# and <tt>:enddoc:</tt> may appear in a stand-alone comment:
#
#   /* :startdoc: */
#   /* :stopdoc: */
#   /* :enddoc: */
#
# ===== Directive for Specifying \RDoc Source Format
#
# - <tt># :markup: _type_</tt>:
#
#   - Appears on a line by itself.
#   - Specifies the format for the \RDoc input;
#     parameter +type+ is one of +markdown+, +rd+, +rdoc+, +tomdoc+.
#
# ===== Directives for HTML Output
#
# - <tt># :title: _text_</tt>:
#
#   - Appears on a line by itself.
#   - Specifies the title for the HTML output.
#
# - <tt># :main: _filename_</tt>:
#   - Appears on a line by itself.
#   - Specifies the HTML file to be displayed first.
#
# ===== Directives for Method Documentation
#
# - <tt># :call-seq:</tt>:
#
#   - Appears on a line by itself.
#   - Specifies the calling sequence to be reported in the HTML,
#     overriding the actual calling sequence in the code.
#     See method #call_seq_directive.
#
#   Note that \RDoc can build the calling sequence for a Ruby-coded method,
#   but not for other languages.
#   You may want to override that by explicitly giving a <tt>:call-seq:</tt>
#   directive if you want to include:
#
#   - A return type, which is not automatically inferred.
#   - Multiple calling sequences.
#
#   For C code, the directive may appear in a stand-alone comment.
#
# - <tt># :args: _arg_names_</tt> (aliased as <tt>:arg:</tt>):
#
#   - Appears on a line by itself.
#   - Specifies the arguments to be reported in the HTML,
#     overriding the actual arguments in the code.
#     See method #args_directive.
#
# - <tt># :yields: _arg_names_</tt> (aliased as <tt>:yield:</tt>):
#
#   - Appears on a line by itself.
#   - Specifies the yield arguments to be reported in the HTML,
#     overriding the actual yield in the code.
#     See method #yields_directive.
#
# ===== Directives for Organizing Documentation
#
# By default, \RDoc groups:
#
# - Singleton methods together in alphabetical order.
# - Instance methods and their aliases together in alphabetical order.
# - Attributes and their aliases together in alphabetical order.
#
# You can use directives to modify those behaviors.
#
# - <tt># :section: _section_title_</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that following methods are to be grouped into the section
#     with the given <em>section_title</em>,
#     or into the default section if no title is given.
#     The directive remains in effect until another such directive is given,
#     but may be temporarily overridden by directive <tt>:category:</tt>.
#     See below.
#
#   The comment block containing this directive:
#
#   - Must be separated by a blank line from the documentation for the next item.
#   - May have one or more lines preceding the directive.
#     These will be removed, along with any trailing lines that match them.
#     Such lines may be visually helpful.
#   - Lines of text that are not so removed become the descriptive text
#     for the section.
#
#   Example:
#
#     # ----------------------------------------
#     # :section: My Section
#     # This is the section that I wrote.
#     # See it glisten in the noon-day sun.
#     # ----------------------------------------
#
#     ##
#     # Comment for some_method
#     def some_method
#       # ...
#     end
#
#   You can use directive <tt>:category:</tt> to temporarily
#   override the current section.
#
# - <tt># :category: _section_title_</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that just one following method is to be included
#     in the given section, or in the default section if no title is given.
#     Subsequent methods are to be grouped into the current section.
#
# ===== Directive for Including a File
#
# - <tt># :include: _filepath_</tt>:
#
#   - Appears on a line by itself.
#   - Specifies that the contents of the given file
#     are to be included at this point.
#     The file content is shifted to have the same indentation as the colon
#     at the start of the directive.
#
#     The file is searched for in the directories
#     given with the <tt>--include</tt> command-line option,
#     or by default in the current directory.
#
#   For C code, the directive may appear in a stand-alone comment
#
# ==== Text Markup
#
# Text markup is metatext that affects HTML rendering:
#
# - Typeface: italic, bold, monofont.
# - Character conversions: copyright, trademark, certain punctuation.
# - Links.
# - Escapes: marking text as "not markup."
#
# ===== Typeface Markup
#
# Typeface markup can specify that text is to be rendered
# as italic, bold, or monofont.
#
# Typeface markup may contain only one type of nested block:
#
# - More typeface markup:
#   italic, bold, monofont.
#
# ====== Italic
#
# Text may be marked as italic via HTML tag <tt><i></tt> or <tt><em></tt>.
#
# Example input:
#
#   <i>Italicized words</i> in a paragraph.
#
#   >>>
#     <i>Italicized words in a block quote</i>.
#
#   - <i>Italicized words</i> in a list item.
#
#   ====== <i>Italicized words</i> in a Heading
#
#   <i>Italicized passage containing *bold* and +monofont+.</i>
#
# Rendered HTML:
# >>>
#   <i>Italicized words</i> in a paragraph.
#
#   >>>
#     <i>Italicized words in a block quote</i>.
#
#   - <i>Italicized words</i> in a list item.
#
#   ====== <i>Italicized words</i> in a Heading
#
#   <i>Italicized passage containing *bold* and +monofont+.</i>
#
# A single word may be italicized via a shorthand:
# prefixed and suffixed underscores.
#
# Example input:
#
#   _Italic_ in a paragraph.
#
#   >>>
#     _Italic_ in a block quote.
#
#   - _Italic_ in a list item.
#
#   ====== _Italic_ in a Heading
#
# Rendered HTML:
# >>>
#   _Italic_ in a paragraph.
#
#   >>>
#     _Italic_ in a block quote.
#
#   - _Italic_ in a list item.
#
#   ====== _Italic_ in a Heading
#
# ====== Bold
#
# Text may be marked as bold via HTML tag <tt><b></tt>.
#
# Example input:
#
#   <b>Bold words</b> in a paragraph.
#
#   >>>
#     <b>Bold words</b> in a block quote.
#
#   - <b>Bold words</b> in a list item.
#
#   ====== <b>Bold words</b> in a Heading
#
#   <b>Bold passage containing _italics_ and +monofont+.</b>
#
# Rendered HTML:
#
# >>>
#   <b>Bold words</b> in a paragraph.
#
#   >>>
#     <b>Bold words</b> in a block quote.
#
#   - <b>Bold words</b> in a list item.
#
#   ====== <b>Bold words</b> in a Heading
#
#   <b>Bold passage containing _italics_ and +monofont+.</b>
#
# A single word may be made bold via a shorthand:
# prefixed and suffixed asterisks.
#
# Example input:
#
#   *Bold* in a paragraph.
#
#   >>>
#     *Bold* in a block quote.
#
#   - *Bold* in a list item.
#
#   ===== *Bold* in a Heading
#
# Rendered HTML:
#
# >>>
#   *Bold* in a paragraph.
#
#   >>>
#     *Bold* in a block quote.
#
#   - *Bold* in a list item.
#
#   ===== *Bold* in a Heading
#
# ====== Monofont
#
# Text may be marked as monofont
# -- sometimes called 'typewriter font' --
# via HTML tag <tt><tt></tt> or <tt><code></tt>.
#
# Example input:
#
#   <tt>Monofont words</tt> in a paragraph.
#
#   >>>
#     <tt>Monofont words</tt> in a block quote.
#
#   - <tt>Monofont words</tt> in a list item.
#
#   ====== <tt>Monofont words</tt> in heading
#
#   <tt>Monofont passage containing _italics_ and *bold*.</tt>
#
# Rendered HTML:
#
# >>>
#   <tt>Monofont words</tt> in a paragraph.
#
#   >>>
#     <tt>Monofont words</tt> in a block quote.
#
#   - <tt>Monofont words</tt> in a list item.
#
#   ====== <tt>Monofont words</tt> in heading
#
#   <tt>Monofont passage containing _italics_ and *bold*.</tt>
#
# A single word may be made monofont by a shorthand:
# prefixed and suffixed plus-signs.
#
# Example input:
#
#   +Monofont+ in a paragraph.
#
#   >>>
#     +Monofont+ in a block quote.
#
#   - +Monofont+ in a list item.
#
#   ====== +Monofont+ in a Heading
#
# Rendered HTML:
#
# >>>
#   +Monofont+ in a paragraph.
#
#   >>>
#     +Monofont+ in a block quote.
#
#   - +Monofont+ in a list item.
#
#   ====== +Monofont+ in a Heading
#
# ==== Character Conversions
#
# Certain combinations of characters may be converted to special characters;
# whether the conversion occurs depends on whether the special character
# is available in the current encoding.
#
# - <tt>(c)</tt> converts to (c) (copyright character); must be lowercase.
#
# - <tt>(r)</tt> converts to (r) (registered trademark character); must be lowercase.
#
# - <tt>'foo'</tt> converts to 'foo' (smart single-quotes).
#
# - <tt>"foo"</tt> converts to "foo" (smart double-quotes).
#
# - <tt>foo ... bar</tt> converts to foo ... bar (1-character ellipsis).
#
# - <tt>foo -- bar</tt> converts to foo -- bar (1-character en-dash).
#
# - <tt>foo --- bar</tt> converts to foo --- bar (1-character em-dash).
#
# ==== Links
#
# Certain strings in \RDoc text are converted to links.
# Any such link may be suppressed by prefixing a backslash.
# This section shows how to link to various
# targets.
#
# [Class]
#
#   - On-page: <tt>DummyClass</tt> links to DummyClass.
#   - Off-page: <tt>RDoc::Alias</tt> links to RDoc::Alias.
#
# [Module]
#
#   - On-page: <tt>DummyModule</tt> links to DummyModule.
#   - Off-page: <tt>RDoc</tt> links to RDoc.
#
# [Constant]
#
#   - On-page: <tt>DUMMY_CONSTANT</tt> links to DUMMY_CONSTANT.
#   - Off-page: <tt>RDoc::Text::MARKUP_FORMAT</tt> links to RDoc::Text::MARKUP_FORMAT.
#
# [Singleton Method]
#
#   - On-page: <tt>::dummy_singleton_method</tt> links to ::dummy_singleton_method.
#   - Off-page<tt>RDoc::TokenStream::to_html</tt> links to RDoc::TokenStream::to_html.
#
#   Note: Occasionally \RDoc is not linked to a method whose name
#   has only special characters. Check whether the links you were expecting
#   are actually there.  If not, you'll need to put in an explicit link;
#   see below.
#
#   Pro tip: The link to any method is available in the alphabetical table of contents
#   at the top left of the page for the class or module.
#
# [Instance Method]
#
#   - On-page: <tt>#dummy_instance_method</tt> links to #dummy_instance_method.
#   - Off-page: <tt>RDoc::Alias#html_name</tt> links to RDoc::Alias#html_name.
#
#     See the Note and Pro Tip immediately above.
#
# [Attribute]
#
#   - On-page: <tt>#dummy_attribute</tt> links to #dummy_attribute.
#   - Off-page: <tt>RDoc::Alias#name</tt> links to RDoc::Alias#name.
#
# [Alias]
#
#   - On-page: <tt>#dummy_instance_alias</tt> links to #dummy_instance_alias.
#   - Off-page: <tt>RDoc::Alias#new_name</tt> links to RDoc::Alias#new_name.
#
# [Protocol +http+]
#
#   - Linked: <tt>http://yahoo.com</tt> links to http://yahoo.com.
#
# [Protocol +https+]
#
#   - Linked: <tt>https://github.com</tt> links to https://github.com.
#
# [Protocol +www+]
#
#   - Linked: <tt>www.yahoo.com</tt> links to www.yahoo.com.
#
# [Protocol +ftp+]
#
#   - Linked: <tt>ftp://nosuch.site</tt> links to ftp://nosuch.site.
#
# [Protocol +mailto+]
#
#   - Linked:  <tt>mailto:/foo@bar.com</tt> links to mailto://foo@bar.com.
#
# [Protocol +irc+]
#
#   - link: <tt>irc://irc.freenode.net/ruby</tt> links to irc://irc.freenode.net/ruby.
#
# [Image Filename Extensions]
#
#   - Link: <tt>https://www.ruby-lang.org/images/header-ruby-logo@2x.png</tt> is
#     converted to an in-line HTML +img+ tag, which displays the image in the HTML:
#
#     https://www.ruby-lang.org/images/header-ruby-logo@2x.png
#
#     Also works for +bmp+, +gif+, +jpeg+, and +jpg+ files.
#
#     Note: Works only for a fully qualified URL.
#
# [Heading]
#
#   - Link: <tt>RDoc::RD@LICENSE</tt> links to RDoc::RDoc::RD@LICENSE.
#
#   Note that spaces in the actual heading are represented by <tt>+</tt> characters
#   in the linkable text.
#
#   - Link: <tt>RDoc::Options@Saved+Options</tt>
#     links to RDoc::Options@Saved+Options.
#
#   Punctuation and other special characters must be escaped like CGI.escape.
#
#   Pro tip: The link to any heading is available in the alphabetical table of contents
#   at the top left of the page for the class or module.
#
# [Section]
#
#   See {Directives for Organizing Documentation}[#class-RDoc::MarkupReference-label-Directives+for+Organizing+Documentation].
#
#   - Link: <tt>RDoc::Markup::ToHtml@Visitor</tt> links to RDoc::Markup::ToHtml@Visitor.
#
#   If a section and a heading share the same name, the link target is the section.
#
# [Single-Word Text Link]
#
#   Use square brackets to create single-word text link:
#
#   - <tt>GitHub[https://github.com]</tt> links to GitHub[https://github.com].
#
# [Multi-Word Text Link]
#
#   Use square brackets and curly braces to create a multi-word text link.
#
#   - <tt>{GitHub home page}[https://github.com]</tt> links to
#     {GitHub home page}[https://github.com].
#
# [<tt>rdoc-ref</tt> Scheme]
#
#   A link with the <tt>rdoc-ref:</tt> scheme links to the referenced item,
#   if that item exists.
#   The referenced item may be a class, module, method, file, etc.
#
#   - Class: <tt>Alias[rdoc-ref:RDoc::Alias]</tt> links to Alias[rdoc-ref:RDoc::Alias].
#   - Module: <tt>RDoc[rdoc-ref:RDoc]</tt> links to RDoc[rdoc-ref:RDoc].
#   - Method: <tt>foo[rdoc-ref:RDoc::Markup::ToHtml#handle_regexp_RDOCLINK]</tt>
#     links to foo[rdoc-ref:RDoc::Markup::ToHtml#handle_regexp_RDOCLINK].
#   - Constant: <tt>bar[rdoc-ref:RDoc::Markup::ToHtml::LIST_TYPE_TO_HTML]</tt>
#     links to bar[rdoc-ref:RDoc::Markup::ToHtml::LIST_TYPE_TO_HTML].
#   - Attribute: <tt>baz[rdoc-ref:RDoc::Markup::ToHtml#code_object]</tt>
#     links to baz[rdoc-ref:RDoc::Markup::ToHtml#code_object].
#   - Alias: <tt>bad[rdoc-ref:RDoc::MarkupReference#dummy_instance_alias]</tt> links to
#     bad[rdoc-ref:RDoc::MarkupReference#dummy_instance_alias].
#
#   If the referenced item does not exist, no link is generated
#   and entire <tt>rdoc-ref:</tt> square-bracketed clause is removed
#   from the resulting text.
#
#   - <tt>Nosuch[rdoc-ref:RDoc::Nosuch]</tt> is rendered as
#     Nosuch[rdoc-ref:RDoc::Nosuch].
#
#
# [<tt>rdoc-label</tt> Scheme]
#
#   [Simple]
#
#     You can specify a link target using this form,
#     where the second part cites the id of an HTML element.
#
#     This link refers to the constant +DUMMY_CONSTANT+ on this page:
#
#     - <tt>{DUMMY_CONSTANT}[rdoc-label:DUMMY_CONSTANT]</tt>
#
#     Thus:
#
#     {DUMMY_CONSTANT}[rdoc-label:DUMMY_CONSTANT]
#
#   [With Return]
#
#     You can specify both a link target and a local label
#     that can be used as the target for a return link.
#     These two links refer to each other:
#
#     - <tt>{go to addressee}[rdoc-label:addressee:sender]</tt>
#     - <tt>{return to sender}[rdoc-label:sender:addressee]</tt>
#
#     Thus:
#
#     {go to addressee}[rdoc-label:addressee:sender]
#
#     Some text.
#
#     {return to sender}[rdoc-label:sender:addressee]
#
# [<tt>link:</tt> Scheme]
#
#   - <tt>link:README_rdoc.html</tt> links to link:README_rdoc.html.
#
# [<tt>rdoc-image</tt> Scheme]
#
#   Use the <tt>rdoc-image</tt> scheme to display an image that is also a link:
#
#     # {rdoc-image:path/to/image}[link_target]
#
#   - Link: <tt>{rdoc-image:https://www.ruby-lang.org/images/header-ruby-logo@2x.png}[https://www.ruby-lang.org]</tt>
#     displays image <tt>https://www.ruby-lang.org/images/header-ruby-logo@2x.png</tt>
#     as a link to <tt>https://www.ruby-lang.org</tt>.
#
#     {rdoc-image:https://www.ruby-lang.org/images/header-ruby-logo@2x.png}[https://www.ruby-lang.org]
#
#   A relative path as the target also works:
#
#   - Link: <tt>{rdoc-image:https://www.ruby-lang.org/images/header-ruby-logo@2x.png}[./Alias.html]</tt> links to <tt>./Alias.html</tt>
#
#     {rdoc-image:https://www.ruby-lang.org/images/header-ruby-logo@2x.png}[./Alias.html]
#
# === Escaping Text
#
# Text that would otherwise be interpreted as markup
# can be "escaped," so that it is not interpreted as markup;
# the escape character is the backslash (<tt>'\\'</tt>).
#
# In a verbatim text block or a code block,
# the escape character is always preserved:
#
# Example input:
#
#   This is not verbatim text.
#
#     This is verbatim text, with an escape character \.
#
#   This is not a code block.
#
#     def foo
#       'String with an escape character.'
#     end
#
# Rendered HTML:
#
# >>>
#   This is not verbatim text.
#
#     This is verbatim text, with an escape character \.
#
#   This is not a code block.
#
#     def foo
#       'This is a code block with an escape character \.'
#     end
#
# In typeface markup (italic, bold, or monofont),
# an escape character is preserved unless it is immediately
# followed by nested typeface markup.
#
# Example input:
#
#   This list is about escapes; it contains:
#
#   - <tt>Monofont text with unescaped nested _italic_</tt>.
#   - <tt>Monofont text with escaped nested \_italic_</tt>.
#   - <tt>Monofont text with an escape character \</tt>.
#
# Rendered HTML:
#
# >>>
#   This list is about escapes; it contains:
#
#   - <tt>Monofont text with unescaped nested _italic_</tt>.
#   - <tt>Monofont text with escaped nested \_italic_</tt>.
#   - <tt>Monofont text with an escape character \ </tt>.
#
# In other text-bearing blocks
# (paragraphs, block quotes, list items, headings):
#
# - A single escape character immediately followed by markup
#   escapes the markup.
# - A single escape character followed by whitespace is preserved.
# - A single escape character anywhere else is ignored.
# - A double escape character is rendered as a single backslash.
#
#   Example input:
#
#     This list is about escapes; it contains:
#
#     - An unescaped class name, RDoc, that will become a link.
#     - An escaped class name, \RDoc, that will not become a link.
#     - An escape character followed by whitespace \ .
#     - An escape character \that is ignored.
#     - A double escape character \\ that is rendered
#       as a single backslash.
#
#   Rendered HTML:
#
#   >>>
#     This list is about escapes; it contains:
#
#     - An unescaped class name, RDoc, that will become a link.
#     - An escaped class name, \RDoc, that will not become a link.
#     - An escape character followed by whitespace \ .
#     - An escape character \that is ignored.
#     - A double escape character \\ that is rendered
#       as a single backslash.
#
# == Documentation Derived from Ruby Code
#
# [Class]
#
#   By default, \RDoc documents:
#
#   - \Class name.
#   - Parent class.
#   - Singleton methods.
#   - Instance methods.
#   - Aliases.
#   - Constants.
#   - Attributes.
#
# [Module]
#
#   By default, \RDoc documents:
#
#   - \Module name.
#   - \Singleton methods.
#   - Instance methods.
#   - Aliases.
#   - Constants.
#   - Attributes.
#
# [Method]
#
#   By default, \RDoc documents:
#
#   - \Method name.
#   - Arguments.
#   - Yielded values.
#
#   See #method.
#
# [Alias]
#
#   By default, \RDoc documents:
#
#   - Alias name.
#   - Aliased name.
#
#   See #dummy_instance_alias and #dummy_instance_method.
#
# [Constant]
#
#   By default, \RDoc documents:
#
#   - \Constant name.
#
#   See DUMMY_CONSTANT.
#
# [Attribute]
#
#   By default, \RDoc documents:
#
#   - Attribute name.
#   - Attribute type (<tt>[R]</tt>, <tt>[W]</tt>, or <tt>[RW]</tt>)
#
#   See #dummy_attribute.
#
class RDoc::MarkupReference

  # Example class.
  class DummyClass; end

  # Example module.
  module DummyModule; end

  # Example singleton method.
  def self.dummy_singleton_method(foo, bar); end

  # Example instance method.
  def dummy_instance_method(foo, bar); end;

  alias dummy_instance_alias dummy_instance_method

  # Example attribute.
  attr_accessor :dummy_attribute

  alias dummy_attribute_alias dummy_attribute

  # Example constant.
  DUMMY_CONSTANT = ''

  # :call-seq:
  #   call_seq_directive(foo, bar)
  #   Can be anything -> bar
  #   Also anything more -> baz or bat
  #
  # The <tt>:call-seq:</tt> directive overrides the actual calling sequence
  # found in the Ruby code.
  #
  # - It can specify anything at all.
  # - It can have multiple calling sequences.
  #
  # This one includes <tt>Can be anything -> foo</tt>, which is nonsense.
  #
  # Note that the "arrow" is two characters, hyphen and right angle-bracket,
  # which is made into a single character in the HTML.
  #
  # Click on the calling sequence to see the code.
  #
  # Here is the <tt>:call-seq:</tt> directive given for the method:
  #
  #   :call-seq:
  #     call_seq_directive(foo, bar)
  #     Can be anything -> bar
  #     Also anything more -> baz or bat
  #
  def call_seq_directive
    nil
  end

  # The <tt>:args:</tt> directive overrides the actual arguments found in the Ruby code.
  #
  # Click on the calling sequence to see the code.
  #
  def args_directive(foo, bar) # :args: baz
    nil
  end

  # The <tt>:yields:</tt> directive overrides the actual yield found in the Ruby code.
  #
  # Click on the calling sequence to see the code.
  #
  def yields_directive(foo, bar) # :yields: 'bat'
    yield 'baz'
  end

  # This method is documented only by \RDoc, except for these comments.
  #
  # Click on the calling sequence to see the code.
  #
  def method(foo, bar)
    yield 'baz'
  end

end