Pod

Pod is an easy-to-use markup language with a simple, consistent underlying document object model. Pod can be used for writing language documentation, for documenting programs and modules, as well as for other types of document composition.

Pod is an evolution of Perl 5's Plain Ol' Documentation (POD) markup. Compared to POD, Perl 6's Pod is much more uniform, somewhat more compact, and considerably more expressive. The Pod dialect also differs in that it is a purely descriptive mark-up notation, with no presentational components.

General syntactic structure

Pod documents are specified using directives, which are used to declare configuration information and to delimit blocks of textual content. All Pod directives are considered to be special types of comments in Perl 6.

Every directive starts either with an equals sign (=) followed immediately by an identifier [1], or with a #= or #| followed immediately by whitespace or an opening bracket.

Directives that start with = can be indented like the code they interleave, but their initial = must still be the first non-whitespace character on their line. Directives that start with #= or #| can be placed anywhere that a Perl 6 comment can appear, though they are meaningful only in a subset of those places; see Declarator blocks.

An indented Pod block is considered to have a virtual left margin, determined by the indentation of its opening delimiter.

In other words, if a directive is indented from the left margin, the column at which the first character of its opening delimiter appears is thereafter considered the first column of the entire block's contents.

As with Perl 6 heredocs, the virtual margin treats leading tabs as aligning to tabstops spaced every ($?TABSTOP // 8) characters.

Pod blocks

The content of a document is specified within one or more blocks. Every Pod block may be declared in any of four forms:

delimited style, paragraph style, abbreviated style, or declarator style. The first three forms are all equivalent; the fourth is distinct.

Anything in a document that is neither a Pod directive nor contained within a Pod block is treated as "ambient" material. Typically this would be the source code of the program that the Pod is documenting. Pod parsers still parse this text into the internal representation of the file, representing it as a Pod::Block::Ambient block. Renderers will usually ignore such blocks, but see Aliases.

In Perl 5's POD format, once a POD directive is encountered, the parser considers everything that follows to be POD, until an explicit =cut directive is encountered, at which point the parser flips back to parsing ambient source code. The Perl 6 Pod format is different. All Pod directives have a defined terminator and the Pod parser always reverts to "ambient" at the end of each Pod directive or block. To cause the parser to remain in Pod mode, you must enclose the desired Pod region in a pod block:

    =begin pod

    =head1 A heading

    This is Pod too. Specifically, this is a simple C<para> block

        $this = pod('also');  # Specifically, a code block

    =end pod

Delimited blocks

Delimited blocks are bounded by =begin and =end markers, both of which are followed by a valid Perl 6 identifier, which is the typename of the block. Typenames that are entirely lowercase (for example: =begin head1) or entirely uppercase (for example: =begin SYNOPSIS) are reserved.

After the typename, the rest of the =begin marker line is treated as configuration information for the block. This information is used in different ways by different types of blocks, but is always specified using Perl6-ish option pairs. That is, any of:

All option keys and values must, of course, be constants since Pod is a specification language, not a programming language. Specifically, option values cannot be closures. See Synopsis 2 for details of the various Perl 6 pair notations.

The configuration section may be extended over subsequent lines by starting those lines with an = in the first (virtual) column followed by a whitespace character.

The lines following the opening delimiter and configuration are the data or contents of the block, which continue until the block's matching =end marker line. For most block types, these contents may be indented if you wish, without them being treated as code blocks. Unlike Perl 5, indented text is only treated as code within =pod, =nested, =item, =code, and semantic blocks.

The general syntax is:

     =begin BLOCK_TYPE  OPTIONAL CONFIG INFO
     =                  OPTIONAL EXTRA CONFIG INFO
     BLOCK CONTENTS
     =end BLOCK_TYPE

For example:

     =begin table  :caption<Table of Contents>
         Constants           1

         Variables           10

         Subroutines         33

         Everything else     57
     =end table

        =begin Name  :required
        =            :width(50)
        The applicant's full name
        =end Name

        =begin Contact  :optional
            The applicant's contact details
        =end Contact

Note that no blank lines are required around the directives; blank lines within the contents are always treated as part of the contents. This is a universal feature of Pod.

Note also that in the following specifications, a "blank line" is a line that is either empty or that contains only whitespace characters. That is, a blank line matches the Perl 6 pattern: /^^ \h* $$/. Pod uses blank lines as delimiters, rather than empty lines, to minimize unpleasant surprises when stray spaces or tabs mysteriously turn up in hitherto empty lines.

Paragraph blocks

Paragraph blocks are introduced by a =for marker and terminated by the next Pod directive or the first blank line (which is not considered to be part of the block's contents). The =for marker is followed by the name of the block and optional configuration information. The general syntax is:

     =for BLOCK_TYPE  OPTIONAL CONFIG INFO
     =                OPTIONAL EXTRA CONFIG INFO
     BLOCK DATA

For example:

     =for table  :caption<Table of Contents>
         Constants           1
         Variables           10
         Subroutines         33
         Everything else     57

        =for Name  :required
        =          :width(50)
        The applicant's full name

     =for Contact  :optional
        The applicant's contact details

Abbreviated blocks

Abbreviated blocks are introduced by an '=' sign in the first column, which is followed immediately by the typename of the block. The rest of the line is treated as block data, rather than as configuration. The content terminates at the next Pod directive or the first blank line (which is not part of the block data). The general syntax is:

     =BLOCK_TYPE  BLOCK DATA
     MORE BLOCK DATA

For example:

     =table
         Constants           1
         Variables           10
         Subroutines         33
         Everything else     57

        =Name  The applicant's full name
     =Contact  The applicant's contact details

Note that abbreviated blocks cannot specify configuration information. If configuration is required, use a =for or =begin/=end instead.

Declarator blocks

The fourth form of Pod block differs from the first three in that it does not specify an explicit typename. Instead, it obtains its identity and purpose from the Perl 6 source code to which it is attached; specifically, from some nearby declarator.

Declarator blocks are introduced by a special Perl comment: either #= or #|, which must be immediately followed by either by a space or an opening bracket. If followed by a space, the block is terminated by the end of line; if followed by one or more opening brackets, the block is terminated by the matching sequence of closing brackets.

That is, declarator Pod blocks are syntactically like ordinary Perl 6 single-line comments and embedded comments. The general syntax is:

     #| BLOCK DATA TO END OF LINE

     #|{ BLOCK DATA
         MORE BLOCK DATA
       }

     #= BLOCK DATA TO END OF LINE

     #={ BLOCK DATA
         MORE BLOCK DATA
       }

except that the bracketed forms may use any valid Perl 6 bracket delimiter (including repeated opening brackets), as described in Synopsis 2.

Declarator Pod blocks must either precede or immediately follow a valid Perl 6 declarator, and are then said to be "attached" to it. They are primarily intended to simplify the documentation of code interfaces.

Declarator blocks that start with #| attach to the declarator immediately after them (separated only by whitespace). Declarator blocks that start with #= attach to the declarator declared at the start of the line immediately before them. In all other respects they act just like comments (i.e. they are themselves whitespace as far as ambient source code is concerned). This means multiple declarator blocks can be specified in a row and will all attach to the same declarator.

For example:

    #| Base class for comms necromancy hierarchy
    class Magic::Necrotelecomnicon {
        has $.elemental;  #= Source of all power
        has $!true_name;  #  Source of all self-protection (not documented)

        method cast(#|{ A spell } Spell $s)
        #= Initiate a specified spell normally
        #= (do not use for class 7 spells)
        {
            do_raw_magic($s);
        }


        method kast(  #= Initiate a specified spell abnormally
            Spell $s     #= The spell to be abnormally initiated
        ) {
            do_raw_magic($s, :alternative);
        }

        #| This subroutine does the real work
        sub do_raw_magic (
            Spell $s,         #= Which spell to invoke
            *%options         #= How to invoke it
        ) {...}
    }

    sub fu (Any $bar)
    #=[ This text stored in C<&fu.WHY>, not in C<$bar.WHY>,
        (because C<sub fu> is the declarator
         at the I<start> of the preceding line)
      ]

    multi sub baz(Int $count, Str $name)
        #=[ This text stored in C<&baz:(Int,Str).WHY>
            (i.e. the C<.WHY> of the variant, not of the entire multisub)
          ]

    #| Attaches to the specific parameterized role, rather than the role group itself
    role R[::T] {}
    role R {}

A declarator can have multiple leading and/or trailing Pod comments, in which case they are concatenated with an intermediate newline when their object's .WHY return value is stringified:

#| This is a special chainsaw
#| (Why, you ask?)
my SwissArmy $chainsaw    #= (It has a rocket launcher!)

say $chainsaw.WHY;    # prints: This is a special chainsaw
                      #         (Why, you ask?)
                      #         (It has a rocket launcher!)

The individual leading and trailing Pod comments can be retrieved via the returned Pod object's .leading and .trailing methods:

say $chainsaw.WHY.leading;    # prints: This is a special chainsaw
                                        (Why, you ask?)

say $chainsaw.WHY.trailing;   # prints: (It has a rocket launcher!)

The Pod object representing each Declarator block is still appended to the current surrounding Pod object (e.g. to $=pod at the top level). Each such block representation is an object of class Pod::Block::Declarator, and has a .WHEREFORE method that returns the code object or metaobject created by the declarator to which the documentation is attached.

In other words, .WHY and .WHEREFORE are inverse operations:

                            .WHY
                 ----------------------------
                |                            |
                |                            v
        -----------------            -----------------
        | Declared code |            | Documentation |
        |    object     |            |    object     |
        -----------------            -----------------
                ^                            |
                |                            |
                 ----------------------------
                         .WHEREFORE

When the default DOC INIT block renders these Pod objects, it automatically includes information about the declarator as well. For instance, the earlier Necrotelecomnicon example might produce something like:

      Name:  Magic::Necrotelecomnicon:
      Desc:  Base class for comms necromancy hierarchy

      Attrs:
           .elemental       : Source of all power

      Methods:
           .cast(Spell $s)  : Initiate a specified spell normally
           .kast(Spell $s)  : Initiate a specified spell abnormally

      Subroutines:
        do_raw_magic(       : This subroutine does the real work
            Spell $s,         : Which spell to invoke
            *%options         : How to invoke it
        )

Note, however, that the exact rendering used for declarator blocks is implementation dependent, and may also be pre-empted explicitly by some DOC configuration statement within the document, such as:

DOC use Pod::Markovian;

or:

DOC INIT {
    use Pod::Eiffelish::Long;

    say eiffelish_long($=pod);

    exit;
}

Block equivalence

The first three block specifications (delimited, paragraph, and abbreviated) are treated identically by the underlying documentation model, so you can use whichever form is most convenient for a particular documentation task. In the descriptions that follow, the abbreviated form will generally be used, but should be read as standing for all three forms equally.

For example, although Headings shows only:

     =head1 Top Level Heading

this automatically implies that you could also write that block as:

     =for head1
     Top Level Heading

or:

     =begin head1
     Top Level Heading
     =end head1

Declarator blocks are distinct from these three forms. They do not have typenames of their own, but rather take their meaning and identity from the declared object or type to which they are attached. In general, they are used specifically to describe that declarand.

Standard configuration options

Pod predefines a small number of standard configuration options that can be applied uniformly to any built-in block type. These include:

C<:nested>

This option specifies that the block is to be nested within its current context. For example, nesting might be applied to block quotes, to textual examples, or to commentaries. In addition the L<C<=code>|#Code blocks>, L<C<=item>|#Lists>, L<C<=input>|#I/O blocks>, and L<C<=output>|#I/O blocks> blocks all have implicit nesting.

Nesting of blocks is usually rendered by adding extra indentation to the block contents, but may also be indicated in other ways: by boxing the contents, by changing the font or size of the nested text, or even by folding the text (so long as a visible placeholder is provided).

Occasionally it is desirable to nest content by more than one level: =begin code =begin para :nested =begin para :nested =begin para :nested "We're going deep, deep, I<deep> undercover!" =end para =end para =end para =end code This can be simplified by giving the C<:nested> option a positive integer value: =begin code :allow<B> =begin para B<:nested(3)> "We're going deep, deep, I<deep> undercover!" =end para =end code You can also give the option a value of zero, to defeat any implicit nesting that might normally be applied to a paragraph. For example, to specify a block of code that should appear I<without> its usual nesting: =begin code :allow<B V> =comment Don't nest this code block in the usual way... B<=begin code :nested(0)>

1 2 3 4 5 6 123456789012345678901234567890123456789012345678901234567890 |------|-----------------------|---------------------------| line instruction comments number code

V<=end code> =end code Note that C<:!nested> could also be used for this purpose: =begin code =Z<>begin code :!nested =end code

C<:numbered>

This option specifies that the block is to be numbered. The most common use of this option is to create L<numbered headings|#Numbered headings> and L<ordered lists|#Ordered lists>, but it can be applied to any block.

The numbering conventions for headings and lists are specified in those sections, but it is up to individual renderers to decide how to display any numbering associated with other types of blocks.

Note that numbering is never explicit; it is always implied by context.

C<:formatted>

This option specifies that the contents of the block should be treated as if they had one or more L<formatting codes|#Formatting codes> placed around them.

For example, instead of: =begin code =for comment The next para is both important and fundamental, so doubly emphasize it...

=begin para B<I< Warning: Do not immerse in water. Do not expose to bright light. Do not feed after midnight. >> =end para =end code you can just write: =begin code :allow<B> =begin para B<:formatted<B I>> Warning: Do not immerse in water. Do not expose to bright light. Do not feed after midnight. =end para =end code The internal representations of these two versions are exactly the same, except that the second one retains the C<:formatted> option information as part of the resulting block object.

Like all formatting codes, codes applied via a C<:formatted> are inherently cumulative. For example, if the block itself is already inside a formatting code, that formatting code will still apply, in addition to the extra "basis" and "important" formatting specified by C<:formatted<B I>>.

C<:like>

This option specifies that a block or config has the same formatting properties as the type named by its value. This is useful for creating related L<configurations|#Block pre-configuration> or for making user-defined synonyms for existing types. For example: =begin code =config head2 :like<head1> :formatted<I>

=config Subhead :like<head2> =end code

C<:allow>

This option expects a list of formatting codes that are to be recognized within any C<V<>> codes that appear in (or are implicitly applied to) the current block. The option is most often used on C<=code> blocks to allow mark-up within those otherwise verbatim blocks, though it can be used in I<any> block that contains verbatim text. See L<#Formatting within code blocks>.

C<:margin>

This option specifies a character that indicates the left margin of the contents of the block. Normally this left margin is determined by the column at which the C<=> of the opening block-delimiter occurs. For example: =begin code =head1 Indenting Pod blocks

=begin para This text is flush with the (virtual) left margin of the Pod block because that margin is implicitly specified by the C<=> of the C<=begin> =end para =end code However, by using the C<:margin> option it is possible to specify a character that acts like an explicit margin when it occurs as the first non-whitespace character on any line within the block. For example: =begin code =head1 Indenting Pod blocks

=begin para :margin<|> |This text is flush with the (virtual) left margin of |the Pod block because that margin is explicitly marked |by the C<|>, as specified by the block's C<:margin<|>> option. =end para =end code The virtual margin can even be to the left of the opening delimiter, which can be convenient to guide subsequent indentations. For example: =begin code sub foo {

V<=begin> pod :margin<|> |=head1 Hey Look: Indented Pod! | |You can indent Pod in Perl 6 |which makes code look cleaner |when documentation is interspersed | | my $this is Code; | |=end pod

... } =end code When a C<:margin> option is used, each subsequent line (until the corresponding closing delimiter is encountered) simply has any text matching C</^^ \s* $margin_char/> automatically removed. This may include a line that then becomes the closing delimiter, as in the above example.

Any line from which such a margin marker is removed automatically resets the implicit margin for subsequent lines of the block, setting it to the length of the "marginalized" indent that was just removed. This implicit margin is then used until the next line with an explicit margin marker is encountered, or the block terminates.

Block types

Pod offers notations for specifying a wide range of standard block types...

Headings

Pod provides an unlimited number of levels of heading, specified by the =headN block marker. For example:

    =head1 A Top Level Heading

      =head2 A Second Level Heading

        =head3 A third level heading

                        =head86 A "Missed it by I<that> much!" heading

While Pod parsers are required to recognize and distinguish all levels of heading, Pod renderers are only required to provide distinct renderings of the first four levels of heading (though they may, of course, provide more than that). Headings at levels without distinct renderings would typically be rendered like the lowest distinctly rendered level.

Numbered headings

You can specify that a heading is numbered using the :numbered option. For example:

    =for head1 :numbered
    The Problem

    =for head1 :numbered
    The Solution

        =for head2 :numbered
        Analysis

            =for head3
            Overview

            =for head3
            Details

        =for head2 :numbered
        Design

    =for head1 :numbered
    The Implementation

which would produce:

It is usually better to preset a numbering scheme for each heading level, in a series of configuration blocks:

    =config head1 :numbered
    =config head2 :numbered
    =config head3 :!numbered

    =head1 The Problem
    =head1 The Solution
    =head2   Analysis
    =head3     Overview
    =head3     Details
    =head2   Design
    =head1 The Implementation

Alternatively, as a short-hand, if the first whitespace-delimited word in a heading consists of a single literal # character, the # is removed and the heading is treated as if it had a :numbered option:

    =head1 # The Problem
    =head1 # The Solution
    =head2   # Analysis
    =head3       Overview
    =head3       Details
    =head2   # Design
    =head1 # The Implementation

Note that, even though renderers are not required to distinctly render more than the first four levels of heading, they are required to correctly honour arbitrarily nested numberings. That is:

    =head6 # The Rescue of the Kobayashi Maru

should produce something like:

Ordinary paragraph blocks

Ordinary paragraph blocks consist of text that is to be formatted into a document at the current level of nesting, with whitespace squeezed, lines filled, and any special inline mark-up applied.

Ordinary paragraphs consist of one or more consecutive lines of text, each of which starts with a non-whitespace character at (virtual) column 1. The paragraph is terminated by the first blank line or block directive. For example:

    =head1 This is a heading block

    This is an ordinary paragraph.
    Its text  will   be     squeezed     and
    short lines filled. It is terminated by
    the first blank line.

    This is another ordinary paragraph.
    Its     text    will  also be squeezed and
    short lines filled. It is terminated by
    the trailing directive on the next line.
        =head2 This is another heading block

        This is yet another ordinary paragraph,
        at the first virtual column set by the
        previous directive

Within a =pod, =item, =defn, =nested, =finish, or semantic block, ordinary paragraphs do not require an explicit marker or delimiters, but there is also an explicit para marker (which may be used anywhere):

     =para
     This is an ordinary paragraph.
     Its text  will   be     squeezed     and
     short lines filled.

and likewise the longer =for and =begin/=end forms. For example:

     =begin para
         This is an ordinary paragraph.
         Its text  will   be     squeezed     and
         short lines filled.

         This is I<still> part of the same paragraph,
         which continues until an...
     =end para

As the previous example implies, when any form of explicit para block is used, any whitespace at the start of each line is removed during rendering. In addition, within a delimited =begin para/=end para block, any blank lines are preserved.

Code blocks

Code blocks are used to specify pre-formatted text (typically source code), which should be rendered without rejustification, without whitespace-squeezing, and without recognizing any inline formatting codes. Code blocks also have an implicit nesting associated with them. Typically these blocks are used to show examples of code, mark-up, or other textual specifications, and are rendered using a fixed-width font.

A code block may be implicitly specified as one or more lines of text, each of which starts with a whitespace character at the block's virtual left margin. The implicit code block is then terminated by a blank line. For example:

    This ordinary paragraph introduces a code block:

        $this = 1 * code('block');
        $which.is_specified(:by<indenting>);

Implicit code blocks may only be used within =pod, =item, =defn, =nested, =finish, or semantic blocks.

There is also an explicit =code block (which can be specified within any other block type, not just =pod, =item, etc.):

     The C<loud_update()> subroutine adds feedback:

        =begin code

        sub loud_update ($who, $status) {
            say "$who -> $status";

            silent_update($who, $status);
        }

        =end code

As the previous example demonstrates, within an explicit =code block the code can start at the (virtual) left margin. Furthermore, lines that start with whitespace characters after that margin have subsequent whitespace preserved exactly (in addition to the implicit nesting of the code). Explicit =code blocks may also contain empty lines.

Formatting within code blocks

Although =code blocks automatically disregard all formatting codes, occasionally you may still need to specify some formatting within a code block. For example, you may wish to emphasize a particular keyword in an example (using a B<> code). Or you may want to indicate that part of the example is metasyntactic (using the R<> code). Or you might need to insert a non-ASCII character (using the E<> code).

You can specify a list of formatting codes that should still be recognized within a code block using the :allow option. The value of the :allow option must be a list of the (single-letter) names of one or more formatting codes. Those codes will then remain active inside the code block. For example:

    =begin code :allow< B R >
    sub demo {
        B<say> 'Hello R<name>';
    }
    =end code

would be rendered:

sub demo {
    say 'Hello name';
}

Note that the use of the :allow option also makes it possible for verbatim formatting codes (such as C<> and V<>) to contain other codes as well.

I/O blocks

Pod also provides blocks for specifying the input and output of programs.

The =input block is used to specify pre-formatted keyboard input, which should be rendered without rejustification or squeezing of whitespace.

The =output block is used to specify pre-formatted terminal or file output which should also be rendered without rejustification or whitespace-squeezing.

Note that, like =code blocks, both =input and =output blocks have an implicit level of nesting. They are also like =code blocks in that they are typically rendered in a fixed-width font, though ideally all three blocks would be rendered in distinct font/weight combinations (for example: regular serifed for code, bold sans-serif for input, and regular sans-serif for output).

Unlike =code blocks, both =input and =output blocks honour any nested formatting codes. This is particularly useful since a sample of input will often include prompts (which are, of course, output). Likewise a sample of output may contain the occasional interactive component. Pod provides special formatting codes (K<> and T<>) to indicate embedded input or output, so you can use the block type that indicates the overall purpose of the sample (i.e. is it demonstrating an input operation or an output sequence?) and then use the "contrasting" formatting code within the block.

For example, to include a small amount of input in a sample of output you could use the K<> formatting code:

    =begin output
        Name:    Baracus, B.A.
        Rank:    Sgt
        Serial:  1PTDF007

        Do you want additional personnel details? K<y>

        Height:  180cm/5'11"
        Weight:  104kg/230lb
        Age:     49

        Print? K<n>
    =end output

Lists

Lists in Pod are specified as a series of contiguous =item blocks. No special "container" directives or other delimiters are required to enclose the entire list. For example:

     The seven suspects are:

     =item  Happy
     =item  Dopey
     =item  Sleepy
     =item  Bashful
     =item  Sneezy
     =item  Grumpy
     =item  Keyser Soze

List items have one implicit level of nesting:

Lists may be multi-level, with items at each level specified using the =item1, =item2, =item3, etc. blocks. Note that =item is just an abbreviation for =item1. For example:

     =item1  Animal
     =item2     Vertebrate
     =item2     Invertebrate

     =item1  Phase
     =item2     Solid
     =item2     Liquid
     =item2     Gas
     =item2     Chocolate

which would be rendered something like:

• Animal

– Vertebrate

– Invertebrate

• Phase

– Solid

– Liquid

– Gas

– Chocolate

Pod parsers must issue a warning if a "level-N+1" =item block (e.g. an =item2, =item3, etc.) appears anywhere except where there is a preceding "level-N" =item in the same surrounding block. That is, an =item3 should only be specified if an =item2 appears somewhere before it, and that =item2 should itself only appear if there is a preceding =item1.

Note that item blocks within the same list are not physically nested. That is, lower-level items should not be specified inside higher-level items:

    =comment WRONG...
    =begin item1          --------------
    The choices are:                    |
    =item2 Liberty        ==< Level 2   |==<  Level 1
    =item2 Death          ==< Level 2   |
    =item2 Beer           ==< Level 2   |
    =end item1            --------------

    =comment CORRECT...
    =begin item1          ---------------
    The choices are:                     |==< Level 1
    =end item1            ---------------
    =item2 Liberty        ==================< Level 2
    =item2 Death          ==================< Level 2
    =item2 Beer           ==================< Level 2

Ordered lists

An item is part of an ordered list if the item has a :numbered configuration option:

     =for item1 :numbered
     Visito

     =for item2 :numbered
     Veni

     =for item2 :numbered
     Vidi

     =for item2 :numbered
     Vici

This would produce something like:

although the numbering scheme is entirely at the discretion of the renderer, so it might equally well be rendered:

or even:

Alternatively, if the first word of the item consists of a single # character, the item is treated as having a :numbered option:

     =item1  # Visito
     =item2     # Veni
     =item2     # Vidi
     =item2     # Vici

To specify an unnumbered list item that starts with a literal #, either make the octothorpe verbatim:

    =item V<#> introduces a comment

or explicitly mark the item itself as being unnumbered:

    =for item :!numbered
    # introduces a comment

The numbering of successive =item1 list items increments automatically, but is reset to 1 whenever any other kind of non-ambient Pod block appears between two =item1 blocks. For example:

    The options are:

    =item1 # Liberty
    =item1 # Death
    =item1 # Beer

    The tools are:

    =item1 # Revolution
    =item1 # Deep-fried peanut butter sandwich
    =item1 # Keg

would produce:

The numbering of nested items (=item2, =item3, etc.) only resets (to 1) when the higher-level item's numbering either resets or increments.

To prevent a numbered =item1 from resetting after a non-item block, you can specify the :continued option:

     =for item1
     # Retreat to remote Himalayan monastery

     =for item1
     # Learn the hidden mysteries of space and time

     I<????>

     =for item1 :continued
     # Prophet!

which produces:

Unordered lists

List items that are not :numbered are treated as defining unordered lists. Typically, such lists are rendered with bullets. For example:

    =item1 Reading
    =item2 Writing
    =item3 'Rithmetic

might be rendered:

•  Reading

—  Writing

¤  'Rithmetic

As with numbering styles, the bulletting strategy used for different levels within a nested list is entirely up to the renderer.

Multi-paragraph list items

Use the delimited form of the =item block to specify items that contain multiple paragraphs. For example:

     Let's consider two common proverbs:

     =begin item :numbered
     I<The rain in Spain falls mainly on the plain.>

     This is a common myth and an unconscionable slur on the Spanish
     people, the majority of whom are extremely attractive.
     =end item

     =begin item :numbered
     I<The early bird gets the worm.>

     In deciding whether to become an early riser, it is worth
     considering whether you would actually enjoy annelids
     for breakfast.
     =end item

     As you can see, folk wisdom is often of dubious value.

which produces:

Definition lists

To create term/definition lists, use a =defn block. This is similar in effect to an =item block, in that a series of =defn blocks implicitly defines a list (but which might then be rendered into HTML using <DL>...</DL> tags, rather than <UL>...</UL> tags)

The first non-blank line of content is treated as a term being defined, and the remaining content is treated as the definition for the term. For example:

    =defn  MAD
    Affected with a high degree of intellectual independence.

    =defn  MEEKNESS
    Uncommon patience in planning a revenge that is worth while.

    =defn
    MORAL
    Conforming to a local and mutable standard of right.
    Having the quality of general expediency.

Like other kinds of list items, definitions can be numbered, using either an option or a leading #:

    =for defn :numbered
    SELFISH
    Devoid of consideration for the selfishness of others.

    =defn # SUCCESS
    The one unpardonable sin against one's fellows.

Nesting blocks

Any block can be nested by specifying a :nested option on it:

    =begin para :nested
        We are all of us in the gutter,E<NL>
        but some of us are looking at the stars!
    =end para

However, qualifying each nested paragraph individually quickly becomes tedious if there are many in a sequence, or if multiple levels of nesting are required:

    =begin para :nested
        We are all of us in the gutter,E<NL>
        but some of us are looking at the stars!
    =end para
    =begin para :nested(2)
            -- Oscar Wilde
    =end para

So Pod provides a =nested block that marks all its contents as being nested:

    =begin nested
    We are all of us in the gutter,E<NL>
    but some of us are looking at the stars!
        =begin nested
        -- Oscar Wilde
        =end nested
    =end nested

Nesting blocks can contain any other kind of block, including implicit paragraph and code blocks. Note that the relative physical indentation of the blocks plays no role in determining their ultimate nesting. The preceding example could equally have been specified:

    =begin nested
    We are all of us in the gutter,E<NL>
    but some of us are looking at the stars!
    =begin nested
    -- Oscar Wilde
    =end nested
    =end nested

Tables

Simple tables can be specified in Pod using a =table block. The table may be given an associated description or title using the :caption option.

Columns are separated by two or more consecutive whitespace characters (double-space), or by a vertical line (|) or a border intersection (+), either of which must be separated from any content by at least one whitespace character. Note that only one column separator type is allowed in a single line, but different lines are allowed to use different visible column separator types (that style is not recommended). Using a mixture of visible and non-visible column separator types in a table is an error.

Rows can be specified in one of two ways: either one row per line, with no separators; or multiple lines per row with explicit horizontal separators (whitespace, intersections (+), or horizontal lines: -, =, _) between every row. Either style can also have an explicitly separated header row at the top. If rows are using the two-whitespace-character separator, the row cells should be carefully aligned to ensure the table is interpreted as the user intended.

Each individual table cell is separately formatted, as if it were a nested =para. Note that table rows are expected to have the same number of cells.

This means you can create tables compactly, line-by-line:

    =table
        The Shoveller   Eddie Stevens     King Arthur's singing shovel
        Blue Raja       Geoffrey Smith    Master of cutlery
        Mr Furious      Roy Orson         Ticking time bomb of fury
        The Bowler      Carol Pinnsler    Haunted bowling ball

or line-by-line with multi-line headers:

    =table
        Superhero     | Secret          |
                      | Identity        | Superpower
        ==============|=================|================================
        The Shoveller | Eddie Stevens   | King Arthur's singing shovel
        Blue Raja     | Geoffrey Smith  | Master of cutlery
        Mr Furious    | Roy Orson       | Ticking time bomb of fury
        The Bowler    | Carol Pinnsler  | Haunted bowling ball

or with multi-line headers and multi-line data:

    =begin table :caption('The Other Guys')

                        Secret
        Superhero       Identity          Superpower
        =============   ===============   ===================
        The Shoveller   Eddie Stevens     King Arthur's
                                          singing shovel

        Blue Raja       Geoffrey Smith    Master of cutlery

        Mr Furious      Roy Orson         Ticking time bomb
                                          of fury

        The Bowler      Carol Pinnsler    Haunted bowling ball

    =end table

Named blocks

Blocks whose names contain at least one uppercase and one lowercase letter are assumed to be destined for specialized renderers or parser plug-ins. For example:

    =begin Xhtml
    <object type="video/quicktime" data="onion.mov">
    =end Xhtml

or:

    =Image http://www.perlfoundation.org/images/perl_logo_32x104.png

Named blocks are converted by the Pod parser to block objects; specifically, to objects of a subclass of the standard Pod::Block::Named class.

For example, the blocks of the previous example would be converted to objects of the classes Pod::Block::Named::Xhtml and Pod::Block::Named::Image respectively. Both of those classes would be automatically created as subclasses of the Pod::Block::Named class (unless they were already defined in a module loaded via some prior DOC use.

The resulting object's .typename method retrieves the short name of the block type: 'Xhtml', 'Image', etc. The object's .config method retrieves the list of configuration options (if any). The object's .contents method retrieves a list of the block's verbatim contents.

Named blocks for which no explicit class has been defined or loaded are usually not rendered by the standard renderers.

Note that all block names consisting entirely of lowercase or entirely of uppercase letters are reserved. See Semantic blocks.

Pod comments

All Pod blocks are intrinsically Perl 6 comments, but Pod comments are comments that Pod renderers ignore too. That is, they are Pod blocks that are never to be rendered by any renderer. They are, of course, still included in any internal Pod representation, and are accessible via the Pod API...and via the $=pod variable within a Perl 6 program.

Comments are useful for meta-documentation (documenting the documentation):

    =comment Add more here about the algorithm

and for temporarily removing parts of a document:

    =item # Retreat to remote Himalayan monastery

    =item # Learn the hidden mysteries of space and time

    =item # Achieve enlightenment

    =begin comment
    =item # Prophet!
    =end comment

Note that, since the Perl interpreter never executes embedded Pod blocks, comment blocks can also be used as an alternative form of nestable block comments in Perl 6:

    =begin comment
    for @files -> $file {
        shell("rm -rf $file");
    }
    =end comment

The =finish block

The =finish block is special in that all three of its forms (delimited, paragraph, and abbreviated) are terminated only by the end of the current file. That is, neither =finish nor =for finish are terminated by the next blank line, and =end finish has no effect within a =begin finish block. A warning is issued if an explicit =end finish appears within a document.

An =finish block indicates the end-point of any ambient material within the document. This means that the parser will treat all the remaining text in the file as Pod, even if it is not inside an explicit block. In other words, apart from its special end-of-file termination behaviour, an =finish block is in all other respects identical to a =pod block.

Data blocks

Named Pod blocks whose typename is data are the Perl 6 equivalent of the Perl 5 __DATA__ section. The difference is that =data blocks are just regular Pod blocks and may appear anywhere within a source file, and as many times as required.

There is a corresponding variable, $=data, from which each =data block can be retrieved. $=data holds an object that does both the Associative and Positional roles.

Each =data block can be given a :key option, to name it. The contents of any =data block with a key are accessible (as a single string) via the Associative aspect of $=data object. For example:

    =begin data :key<Virtues>
    Laziness
    Impatience
    Hubris
    =end data

    say 'The three virtues are:';
    say $=data<Virtues>;

The contents of any =data block that does not have a :key are accessible (as a single string) via the Positional aspect of $=data. Unkeyed =data blocks are stored in the same order they appear in the file. For example:

    say 'The second anti_Virtue is: ', $=data[1];

    =data Industry
    =data Patience
    =data Humility

Note that, as the preceding example illustrates, because Pod is a compile-time phenomenon, it is possible to specify =data blocks after the point in the source where their contents will be used (provided they're not being used in a BEGIN, of course).

When $=data itself is stringified, it returns the concatenation of all the unkeyed =data blocks the parser has seen.

=data blocks are never rendered by the standard Pod renderers.

Semantic blocks

All uppercase block typenames are reserved for specifying standard documentation, publishing, source components, or meta-information of a compunit it needs to be able to be selected for loading. In particular, all the standard components found in Perl and manpage documentation have reserved uppercase typenames.

Standard semantic blocks include:

    =NAME
    =AUTHOR
    =VERSION
    =CREATED
    =EMULATES
    =EXCLUDES
    =SYNOPSIS
    =DESCRIPTION
    =USAGE
    =INTERFACE
    =METHOD
    =SUBROUTINE
    =OPTION
    =DIAGNOSTIC
    =ERROR
    =WARNING
    =DEPENDENCY
    =BUG
    =SEE-ALSO
    =ACKNOWLEDGEMENT
    =COPYRIGHT
    =DISCLAIMER
    =LICENCE
    =LICENSE
    =TITLE
    =SECTION
    =CHAPTER
    =APPENDIX
    =TOC
    =INDEX
    =FOREWORD
    =SUMMARY

The plural forms of each of these keywords are also reserved, and are aliases for the singular forms.

Most of these blocks would typically be used in their full delimited forms:

    =begin SYNOPSIS
        use Magic::Parser;

        my Magic::Parser $parser .= new();

        my $tree = $parser.parse($fh);
    =end SYNOPSIS

Semantic blocks can be considered to be variants of the =head1 block in most respects (and most renderers will treat them as such). The main difference is that, in a =head1 block, the heading is the contents of the block; whereas, in a semantic block, the heading is derived from the typename of the block itself and the block contents are instead treated as the =para or =code block(s) belonging to the heading.

The use of these special blocks is not required; you can still just write:

    =head1 SYNOPSIS
    =begin code
        use Magic::Parser

        my Magic::Parser $parser .= new();

        my $tree = $parser.parse($fh);
    =end code

However, using the keywords adds semantic information to the documentation, which may assist various renderers, summarizers, coverage tools, document refactorers, and other utilities. This is because a semantic block encloses the text it controls (unlike a =head1, which merely precedes its corresponding text), so using semantic blocks produces a more explicitly structured document.

Note that there is no requirement that semantic blocks be rendered in a particular way (or at all). Specifically, it is not necessary to preserve the capitalization of the keyword. For example, the =SYNOPSIS block of the preceding example might be rendered like so:

    use Perl6::Magic::Parser;

    my $rep = Perl6::Magic::Parser.parse($fh, :all_pod);

Formatting codes

Formatting codes provide a way to add inline mark-up to a piece of text within the contents of (most types of) Pod block (including all declarator blocks). Formatting codes are themselves a type of block, and may nest other formatting codes. other type of block (most often, other formatting codes). In particular, you can nest comment blocks in the middle of a formatting code:

    B<I shall say this loudly
    Z<and repeatedly>
    and with emphasis.>

All Pod formatting codes consist of a single capital letter followed immediately by a set of angle brackets. The brackets contain the text or data to which the formatting code applies. You can use a set of single angles (<...>), a set of double angles («...»), or multiple single-angles (<<<...>>>).

Within angle delimiters, you cannot use sequences of the same angle characters that are longer than the delimiters:

    =comment
        These are errors...

    C< $foo<<bar>> >
    The Perl 5 heredoc syntax was: C< <<END_MARKER >

You can use sequences of angles that are the same length as the delimiters, but they must be balanced. For example:

C<  $foo<bar>   >
C<< $foo<<bar>> >>

If you need an unbalanced angle, either use different delimiters:

    C«$foo < $bar»
    The Perl 5 heredoc syntax was: C« <<END_MARKER »

or delimiters with more consecutive angles than your text contains:

    C<<$foo < $bar>>
    The Perl 5 heredoc syntax was: C<<< <<END_MARKER >>>

A formatting code ends at the matching closing angle bracket(s), or at the end of the enclosing block or formatting code in which the opening angle bracket was specified, whichever comes first (this includes paragraph and abbreviated blocks, ending with blank a line). Pod parsers are required to issue a warning whenever a formatting code is terminated by the end of an outer block rather than by its own delimiter (unless the user explicitly disables the warning).

Significance indicators

Pod provides three formatting codes that flag their contents with increasing levels of significance:

• The U<> formatting code specifies that the contained text is unusual or distinctive; that it is of minor significance. Typically such content would be rendered in an underlined style.

• The I<> formatting code specifies that the contained text is important; that it is of major significance. Such content would typically be rendered in italics or in <em>...</em> tags

• The B<> formatting code specifies that the contained text is the basis or focus of the surrounding text; that it is of fundamental significance. Such content would typically be rendered in a bold style or in <strong>...</strong> tags.

Definitions

The D<> formatting code indicates that the contained text is a definition, introducing a term that the adjacent text elucidates. It is the inline equivalent of a =defn block. For example:

    There ensued a terrible moment of D<coyotus interruptus>: a brief
    suspension of the effects of gravity, accompanied by a sudden
    to-the-camera realization of imminent downwards acceleration.

A definition may be given synonyms, which are specified after a vertical bar and separated by semicolons:

    A D<formatting code|formatting codes;formatters> provides a way
    to add inline mark-up to a piece of text.

A definition would typically be rendered in italics or <dfn>...</dfn> tags and will often be used as a link target for subsequent instances of the term (or any of its specified synonyms) within a hypertext.

Example specifiers

Pod provides formatting codes for specifying inline examples of input, output, code, and metasyntax:

• The T<> formatting code specifies that the contained text is terminal output; that is: something that a program might print out. Such content would typically be rendered in a fixed-width font or with <samp>...</samp> tags. The contents of a T<> code are always space-preserved (as if they had an implicit S<...> around them). The T<> code is the inline equivalent of the =output block.

• The K<> formatting code specifies that the contained text is keyboard input; that is: something that a user might type in. Such content would typically be rendered in a fixed-width font (preferably a different font from that used for the T<> formatting code) or with <kbd>...</kbd> tags. The contents of a K<> code are always space-preserved. The K<> code is the inline equivalent of the =input block.

• The C<> formatting code specifies that the contained text is code; that is, something that might appear in a program or specification. Such content would typically be rendered in a fixed-width font (preferably a different font from that used for the T<> or K<> formatting codes) or with <code>...</code> tags. The contents of a C<> code are space-preserved and verbatim. The C<> code is the inline equivalent of the =code block.

  To include other formatting codes in a C<> code, you can lexically reconfigure it:

      =begin para
      =config C<> :allow<E I>
      Perl 6 makes extensive use of the C<E<laquo>> and C<E<raquo>>
      characters, for example, in a hash look-up:
      C<%hashI<E<laquo>>keyI<E<raquo>>>
      =end para
  

  To enable entities in every C<...> put a =config C<> :allow<E> at the top of the document

• The R<> formatting code specifies that the contained text is a replaceable item, a placeholder, or a metasyntactic variable. It is used to indicate a component of a syntax or specification that should eventually be replaced by an actual value. For example:

      The basic C<ln> command is: C<ln> R<source_file> R<target_file>
  

  or:

      Then enter your details at the prompt:
  
      =for input
          Name: R<your surname>
            ID: R<your employee number>
          Pass: R<your 36-letter password>
  

  Typically replaceables would be rendered in fixed-width italics or with <var>...</var> tags. The font used should be the same as that used for the C<> code, unless the R<> is inside a K<> or T<> code (or the equivalent =input or =output blocks), in which case their respective fonts should be used.

Verbatim text

The V<> formatting code treats its entire contents as being verbatim, disregarding every apparent formatting code within it. For example:

The B<V< V<> >> formatting code disarms other codes
such as V< I<>, C<>, B<>, and M<> >.

Note, however that the V<> code only changes the way its contents are parsed, not the way they are rendered. That is, the contents are still wrapped and formatted like plain text, and the effects of any formatting codes surrounding the V<> code are still applied to its contents. For example the previous example is rendered:

You can prespecify formatting codes that remain active within a V<> code, using the :allow option.

Inline comments

The Z<> formatting code indicates that its contents constitute a zero-width comment, which should not be rendered by any renderer. For example:

    The "exeunt" command Z<Think about renaming this command?> is used
    to quit all applications.

In Perl 5 POD, the Z<> code was widely used to break up text that would otherwise be considered mark-up:

    In Perl 5 POD, the ZZ<><> code was widely used to break up text
    that would otherwise be considered mark-up.

That technique still works, but it's now easier to accomplish the same goal using a verbatim formatting code:

    In Perl 5 POD, the V<V<Z<>>> code was widely used to break up text
    that would otherwise be considered mark-up.

Moreover, the C<> code automatically treats its contents as being verbatim, which often eliminates the need for the V<> as well:

    In Perl 5 POD, the V<C<Z<>>> code was widely used to break up text
    that would otherwise be considered mark-up.

The Z<> formatting code is the inline equivalent of a =comment block.

Comments as category markers

Most Pod renderers will provide a mechanism that allows particular Pod blocks to be explicitly excluded or included if they match a particular pattern. For example, a renderer might be instructed to omit any block that contains the pattern /CONFIDENTIAL/. Corresponding "invisibility markers" can then be placed inside Z<> comments within any block that should not normally be displayed. For example:

    class Widget is Bauble
    {
        has $.things; #= a collection of other stuff
        #={ Z<CONFIDENTIAL>
            This variable needs to be replaced for political reasons
        }
    }

Links

The L<> code is used to specify all kinds of links, filenames, citations, and cross-references (both internal and external).

A link specification consists of a scheme specifier terminated by a colon, followed by an external address (in the scheme's preferred syntax), followed by an internal address (again, in the scheme's syntax). All three components are optional, though at least one must be present in any link specification.

Usually, in schemes where an internal address makes sense, it will be separated from the preceding external address by a #, unless the particular addressing scheme requires some other syntax. When new addressing schemes are created specifically for Pod it is strongly recommended that # be used to mark the start of internal addresses.

Standard schemes include:

C<http:> and C<https:>

A standard web URL. For example: =begin code :allow<B> This module needs the LAME library (available from L<B<http://www.mp3dev.org/mp3/>>) =end code If the link does not start with C<//> it is treated as being relative to the location of the current document: =begin code :allow<B> See also: L<B<http:tutorial/faq.html>> and L<B<http:../examples/index.html>> =end code

C<file:>

A filename on the local system. For example: =begin code :allow<B> Next, edit the global config file (that is, either L<B<file:/usr/local/lib/.configrc>> or L<B<file:~/.configrc>>). =end code Filenames that don't begin with a C</> or a C<~> are relative to the current document's location: =begin code :allow<B> Then, edit the local config file (that is, either L<B<file:.configrc>> or L<B<file:CONFIG/.configrc>>. =end code

C<mailto:>

An email address. Typically, activating this type of link invokes a mailer. For example: =begin code :allow<B> Please forward bug reports to L<B<mailto:[email protected]>> =end code

C<man:>

A link to the system manpages. For example: =begin code :allow<B> This module implements the standard Unix L<B<man:find(1)>> facilities. =end code

C<doc:>

A link to some other documentation, typically a module or part of the core documentation; things that would normally be read with C<perl --doc>. For example: =begin code :allow<B> You may wish to use L<B<doc:Data::Dumper>> to view the results. See also: L<B<doc:perldata>>. =end code

C<defn:>

A link to the L<block-form|#Definition lists> or L<inline|#Definitions> definition of the specified term within the current document. For example: =begin code :allow<B> He was highly prone to B<D<lexiphania>>: an unfortunate proclivity for employing grandiloquisms (for example, words such as "proclivity", "grandiloquism", and indeed "lexiphania").

B<=defn glossoligation> Restraint of the tongue (voluntary or otherwise) =end code and later, to link back to the definition =begin code :allow<B> To treat his chronic L<B<defn:lexiphania>> the doctor prescribed an immediate L<B<defn:glossoligation>> or, if that proved ineffective, a complete cephalectomy. =end code

C<isbn:> and C<issn:>

The International Standard Book Number or International Standard Serial Number for a publication. For example: =begin code :allow<B> The Perl Journal was a registered serial publication (L<B<issn:1087-903X>>) =end code

To refer to a specific section within a webpage, manpage, or Pod document, add the name of that section after the main link, separated by a #. For example:

    Also see: L<man:bash(1)#Compound Commands>,
    L<doc:perlsyn#For Loops>, and
    L<http://dev.perl.org/perl6/syn/S04.html#The_for_statement>

To refer to a section of the current document, omit the external address:

    This mechanism is described under L<doc:#Special Features> below.

The scheme name may also be omitted in that case:

    This mechanism is described under L<#Special Features> below.

Normally a link is presented as some rendered version of the link specification itself. However, you can specify an alternate presentation by prefixing the link with the desired text and a vertical bar. Whitespace is not significant on either side of the bar. For example:

    This module needs the L<LAME library|http://www.mp3dev.org/mp3/>.

    You could also write the code
    L<in Latin | doc:Lingua::Romana::Perligata>

    His L<lexiphanic|defn:lexiphania>> tendencies were, alas, incurable.

Placement links

A second kind of link—the P<> or placement link—works in the opposite direction. Instead of directing focus out to another document, it allows you to assimilate the contents of another document into your own.

In other words, the P<> formatting code takes a URI and (where possible) inserts the contents of the corresponding document inline in place of the code itself.

P<> codes are handy for breaking out standard elements of your documentation set into reusable components that can then be incorporated directly into multiple documents. For example:

might produce:

If a renderer cannot find or access the external data source for a placement link, it must issue a warning and render the URI directly in some form, possibly as an outwards link. For example:

You can use any of the following URI forms (see Links) in a placement link:

• http: and https:

• file:

• man:

• doc:

• toc:

The toc: form is a special pseudo-scheme that inserts a table of contents in place of the P<> code. After the colon, list the block types that you wish to include in the table of contents. For example, to place a table of contents listing only top- and second-level headings:

P<toc: head1 head2>

To place a table of contents that lists the top four levels of headings, as well as any tables:

P<toc: head1 head2 head3 head4 table>

To place a table of diagrams (assuming a user-defined Diagram block):

P<toc: Diagram>

Note also that, for P<toc:...>, all semantic blocks are treated as equivalent to head1 headings, and the =item1/=item equivalence is preserved.

A document may have as many P<toc:...> placements as necessary.

Alias placements

A variation on placement codes is the A<> code, which is replaced by the contents of the named alias or object specified within its delimiters. For example:

    =alias PROGNAME    Earl Irradiatem Eventually
    =alias VENDOR      4D Kingdoms
    =alias TERMS_URL   L<http://www.4dk.com/eie>

    The use of A<PROGNAME> is subject to the terms and conditions
    laid out by A<VENDOR>, as specified at A<TERMS_URL>.

Any compile-time Perl 6 object that starts with a sigil is automatically available within an alias placement as well. Unless the object is already a string type, it is converted to a string during document-generation by implicitly calling .perl on it.

So, for example, a document can refer to its own filename (as A<$?FILE>), or to the subroutine inside which the specific Pod is nested (as A<&?ROUTINE>), or to the current class (as A<$?CLASS>). Similarly, the value of any program constants defined with sigils can be easily reproduced in documentation:

    # Actual code...
    constant Num $GROWTH_RATE = 1.6;

    =pod
    =head4 Standard Growth Rate

    The standard growth rate is assumed to be A<$GROWTH_RATE>.

Non-mutating method calls on these objects are also allowed, so a document can reproduce the surrounding subroutine's signature (A<&?ROUTINE.signature>) or the type of a constant (A<$GROWTH_RATE.WHAT>).

See Aliases for further details of the aliasing macro mechanism.

Space-preserving text

Any text enclosed in an S<> code is formatted normally, except that every whitespace character in it—including any newline—is preserved. These characters are also treated as being non-breaking (except for the newlines, of course). For example:

The emergency signal is: S<
dot dot dot   dash dash dash   dot dot dot>.

would be formatted like so:

rather than:

Entities

To include Unicode code points or HTML5 character references in a Pod document, specify the required entity using the E<> code.

If the E<> contains a number, that number is treated as the decimal Unicode value for the desired code point. For example:

Perl 6 makes considerable use of E<171> and E<187>.

You can also use explicit binary, octal, decimal, or hexadecimal numbers (using the Perl 6 notations for explicitly based numbers):

Perl 6 makes considerable use of E<0b10101011> and E<0b10111011>.
Perl 6 makes considerable use of E<0o253> and E<0o273>.
Perl 6 makes considerable use of E<0d171> and E<0d187>.
Perl 6 makes considerable use of E<0xAB> and E<0xBB>.

If the E<> contains anything that is not a number, the contents are interpreted as a Unicode character name (which is always uppercase), or else as an HTML5 named character reference. For example:

Perl 6 makes considerable use of E<LEFT DOUBLE ANGLE BRACKET>
and E<RIGHT DOUBLE ANGLE BRACKET>.

or, equivalently:

Perl 6 makes considerable use of E<laquo> and E<raquo>.

Multiple consecutive entities (in any format) can be specified in a single E<> code, separated by semicolons:

Perl 6 makes considerable use of E<LEFT DOUBLE ANGLE BRACKET;hellip;0xBB>.

Indexing terms

Anything enclosed in an X<> code is an index entry. The contents of the code are both formatted into the document and used as the (case-insensitive) index entry:

    An X<array> is an ordered list of scalars indexed by number,
    starting with 0. A X<hash> is an unordered collection of scalar
    values indexed by their associated string key.

You can specify an index entry in which the indexed text and the index entry are different, by separating the two with a vertical bar:

    An X<array|arrays> is an ordered list of scalars indexed by number,
    starting with 0. A X<hash|hashes> is an unordered collection of
    scalar values indexed by their associated string key.

In the two-part form, the index entry comes after the bar and is case-sensitive.

You can specify hierarchical index entries by separating indexing levels with commas:

    An X<array|arrays, definition of> is an ordered list of scalars
    indexed by number, starting with 0. A X<hash|hashes, definition of>
    is an unordered collection of scalar values indexed by their
    associated string key.

You can specify two or more entries for a single indexed text, by separating the entries with semicolons:

    A X<hash|hashes, definition of; associative arrays>
    is an unordered collection of scalar values indexed by their
    associated string key.

The indexed text can be empty, creating a "zero-width" index entry:

    X<|puns, deliberate>This is called the "Orcish Manoeuvre"
    because you "OR" the "cache".

Annotations

Anything enclosed in an N<> code is an inline note. For example:

    Use a C<for> loop instead.N<The Perl 6 C<for> loop is far more
    powerful than its Perl 5 predecessor.> Preferably with an explicit
    iterator variable.

Renderers may render such annotations in a variety of ways: as footnotes, as endnotes, as sidebars, as pop-ups, as tooltips, as expandable tags, etc. They are never, however, rendered as unmarked inline text. So the previous example might be rendered as:

and later:

Module-defined formatting codes

Modules loaded with a DOC use can define classes that implement new formatting codes, which can then be specified using the M<> code. An M<> code must start with a colon-terminated scheme specifier. The rest of the enclosed text is treated as the (verbatim) contents of the formatting code. For example:

    DOC use Pod::TT;

    =head1 Overview of the M<TT: $CLASSNAME > class
    (version M<TT: $VERSION>)

    M<TT: get_description($CLASSNAME) >

The M<> formatting code is the inline equivalent of a named block.

Internally an M<> code is converted to an object derived from the Pod::FormattingCode::Named class. The name of the scheme becomes the final component of the object's classname. For instance, the M<> code in the previous example would be converted to a Pod::FormattingCode::Named::TT object, whose .typename method retrieves the string "TT" and whose .contents method retrieves a list of the formatting code's (verbatim, unformatted) contents.

If the formatting code is unrecognized, the contents of the code (i.e. everything after the first colon) would normally be rendered as ordinary text.

Encoding

By default, Pod assumes that documents are Unicode, encoded in one of the three common schemes (UTF-8, UTF-16, or UTF-32). The particular scheme a document uses is autodiscovered by examination of the first few bytes of the file (where possible). If the autodiscovery fails, UTF-8 is assumed, and parsers may treat any non-UTF-8 bytes later in the document as fatal errors.

At any point in a document, you can explicitly set or change the encoding of its content using the =encoding directive:

    =encoding ShiftJIS

    =encoding Macintosh

    =encoding KOI8-R

The specified encoding is used from the start of the next line in the document. If a second =encoding directive is encountered, the current encoding changes again after that line. Note, however, that the second encoding directive must itself be encoded using the first encoding scheme.

This requirement also applies to an =encoding directive at the very beginning of the file. That is, it must itself be encoded in the default UTF-8, -16, or -32. However, as a special case, the autodiscovery mechanism will (as far as possible) also attempt to recognize "self-encoded" =encoding directives that begin at the first byte of the file. For example, at the start of a ShiftJIS-encoded file you can specify =encoding ShiftJIS in the ShiftJIS encoding.

An =encoding directive affects any ambient code between the Pod as well. That is, Perl 6 uses =encoding directives to determine the encoding of its source code as well as that of any documentation.

Note that =encoding is a fundamental Pod directive, like =begin or =for; it is not an instance of an abbreviated block. Hence there is no paragraph or delimited form of the =encoding directive (just as there is no paragraph or delimited form of =begin).

Block pre-configuration

The =config directive allows you to prespecify standard configuration information that is applied to every block of a particular type.

For example, to specify particular formatting for different levels of heading, you could preconfigure all the heading blocks with appropriate formatting schemes:

    =config head1              :formatted<B U>  :numbered
    =config head2 :like<head1> :formatted<I>
    =config head3              :formatted<U>
    =config head4 :like<head3> :formatted<I>

The general syntax for configuration directives is:

    =config BLOCK_TYPE  CONFIG OPTIONS
    =                   OPTIONAL EXTRA CONFIG OPTIONS

Like =encoding, a =config is a directive, not a block. Hence, there is no paragraph or delimited form of the =config directive. Each =config specification is lexically scoped to the surrounding block in which it is specified.

Note that, if a particular block later explicitly specifies a configuration option with the same key, that option overrides the pre-configured option. For example, given the heading configurations in the previous example, to specify a non-basic second-level heading:

    =for head2 :formatted<I U>
    Details

The :like option causes the current formatting options for the named block type to be (lexically) replaced by the complete formatting information of the block type specified as the :like's value. That other block type must already have been preconfigured. Any additional formatting specifications are subsequently added to that config. For example:

    =comment  In the current scope make =head2 an "important" variant of =head1
    =config head2 :like<head1> :formatted<I>

Incidentally, this also means you can arrange for an explicit :formatted option to augment an existing =config, rather than replacing it. Like so:

    =comment  Mark this =head3 (but only this one) as being important
            (in addition to the normal formatting)...
    =head3 :like<head3> :formatted<I>

Pre-configuring formatting codes

You can also lexically preconfigure a formatting code, by naming it with a pair of angles as a suffix. For example:

    =comment  Always allow E<> codes in any (implicit or explicit) V<> code...
    =config V<>  :allow<E>

    =comment  All inline code to be marked as important...
    =config C<>  :formatted<I>

Note that, even though the formatting code is named using single-angles, the preconfiguration applies regardless of the actual delimiters used on subsequent instances of the code.

Aliases

The =alias directive provides a way to define lexically scoped synonyms for longer Pod sequences, (meta)object declarators from the code, or even entire chunks of ambient source. These synonyms can then be inserted into subsequent Pod using the A<> formatting code.

Note that =alias is a fundamental Pod directive, like =begin or =for; there are no equivalent paragraph or delimited forms.

There are two forms of =alias directive: macro aliases and contextual aliases. Both forms are lexically scoped to the surrounding Pod block.

Macro aliases

The simplest form of alias takes two arguments. The first is an identifier (which is usually specified in uppercase, though this is certainly not mandatory). The second argument consists of one or more lines of replacement text.

This creates a lexically scoped Perl 6 macro that can be invoked during document generation by placing the identifier (i.e. the first argument of the alias) in an A<> formatting code. This formatting code is then replaced by the text returned by new macro.

The replacement text returned by the alias macro begins at the first non-whitespace character after the alias's identifier, and continues to the end of the line. You can extend the replacement text over multiple lines by starting the following line(s) with an = (at the same level of indentation as the =alias directive itself) followed by at least one whitespace. Each addition line of replacement text uses the original line's (virtual) left margin, as specified by the indentation of the replacement text on the =alias line.

For example:

    =alias PROGNAME    Earl Irradiatem Evermore
    =alias VENDOR      4D Kingdoms
    =alias TERMS_URLS  =item L<http://www.4dk.com/eie>
    =                  =item L<http://www.4dk.co.uk/eie.io/>
    =                  =item L<http://www.fordecay.ch/canttouchthis>

    The use of A<PROGNAME> is subject to the terms and conditions
    laid out by A<VENDOR>, as specified at:

        A<TERMS_URL>

would produce:

The use of Earl Irradiatem Evermore is subject to the terms and conditions laid out by 4D Kingdoms Inc, as specified at:

The advantage of using aliases is, obviously, that the same alias can be reused in multiple places in the documentation. Then, if the replacement text ever has to be changed, it need only be modified in a single place:

    =alias PROGNAME    Count Krunchem Constantly
    =alias VENDOR      Last Chance Receivers Intl
    =alias TERMS_URLS  L<http://www.c11.com/generic_conditions>

Contextual aliases

If the =alias directive is specified with only a single argument (that is, with only its identifier), a contextual alias is created. In this form, the =alias directive must be followed immediately (on the next non-blank line) by ambient code.

The single argument is then used as the name of the alias being created, and some portion of the following code is used as the value returned by the alias macro.

Note that the code block following the =alias line is still treated as real code by the Perl 6 parser, but its contents are also used to create the replacement macro of the alias. This allows the developer to reproduce chunks of actual source code directly in the documentation, without having to copy it.

If the code following the one-argument =alias directive begins with a sequence of one or more repetitions of any opening bracket character, the replacement macro returns a string containing everything from the end of that opening sequence to just before the corresponding closing bracket sequence. For example:

    # This is actual code...

    sub hash_function ($key)
    =alias HASHCODE
    {
        my $hash = 0;
        for $key.split("") -> $char {
            $hash = $hash*33 + $char.ord;
        }
        return $hash;
    }

    =begin pod
    An ancient (but fast) hashing algorithm is used:

        =begin code :allow<A>
        A<HASHCODE>
        =end code

    =end pod

This would produce:

my $hash = 0;
for $key.split("") -> $char {
    $hash *= 33;
    $hash += $char.ord;
}
return $hash;

Alternatively, if the =alias directive is not followed by an opening bracket, it must be followed by a declarator (such as my, class, sub, etc.) The declared object then becomes the (read-only) return value of the alias. For example:

    =alias CLASSNAME
    class Database::Handle {
        =alias ATTR
        has IO $!handle;

        =alias OPEN
        my Bool method open ($filename?) {...}

        =alias DEFNAME
        constant Str DEFAULT_FILENAME = 'db.log';

        =for para
            Note that the A<OPEN.name> method of class A<CLASSNAME>
            stores the resulting low-level database handle
            in its private A<ATTR.name> attribute. By default,
            handles are opened to the file "A<DEFNAME>".

    }

This would produce:

How Pod is parsed and processed

Pod is just a collection of specialized forms of Perl 6 comment. Every Perl 6 implementation must provide a special command-line flag that locates, parses, and processes Pod to produce documentation. That flag is --doc.

Hence, to read Pod documentation you would type things like:

perl --doc  perlrun

perl --doc  DBI::DBD::Metadata

perl --doc  ./lib/My/Module.pm

When the Perl 6 interpreter is run in this mode, it sets the compiler hint $?DOC to true. If the --doc flag is given a value, that value (with a but true added) is placed in $?DOC. This can be used to specify, for example, the output format desired:

perl --doc=HTML perldelta  > perldelta.html

Under --doc, the interpreter runs in a special mode, parsing the source code (including the Pod, as it always does) during compilation and building the program's syntax tree. However, during parsing and initialization under --doc, the interpreter executes any BEGIN, CHECK, and INIT blocks (and equivalents, such as use statements and subroutine declarations) that are preceded by the special prefix: DOC

When the --doc is not specified on the commandline, blocks and statements that are preceded by the DOC prefix are not executed at all.

By default, once the DOC INIT phase is complete, the interpreter then calls a special default DOC INIT block that walks the AST and generates the documentation, guided by the content of the $?DOC hint, the $=pod tree, and any DOC blocks that have loaded Pod-related handler code.

Because the conversion of documentation is just a variation on the standard Perl 6 compilation process, the processing of any given file of Pod can be modified from within that file itself by the appropriate insertion of DOC blocks. For example:

DOC use Pod::Markovian;

or:

DOC BEGIN {
    use Pod::Literate;

    if ($?DOC ~~ /short/) {
        literate_sequence(<
            NAME
            AUTHOR
            SYNOPSIS
            COPYRIGHT
            WARRANTY
            DESCRIPTION
            INTERFACE
            DIAGNOSTICS
        >);
    }
    else {
        literate_sequence(:default);
    }

You can even replace the standard Pod processor with your own, so long as you remember to exit before the default DOC INIT can run:

DOC INIT {
    use My::Pod::To::Text;

    pod_to_text( $=pod );

    exit(0);
}

The idea is that developers will be able to add their own documentation mechanisms simply by loading a module (via a DOC use) to augment or override the default documentation behaviour. Such mechanisms can then be built using code written in standard Perl 6 that accesses $=pod, as well as using the .WHY and .WHEREFORE introspection methods of any constructs that have attached Pod blocks.

Note also that this mechanism means that, on many systems, you can create a self-converting documentation file like so:

    #! /usr/bin/perl6 --doc

    =begin pod

    =head1 A document that can write itself

    Executing this document from the commandline will automatically
    convert it to a readable text representation.

    =head2 Et cetera
    ...

    =end pod