perlpod - plain old documentation

- NAME
- DESCRIPTION

- Verbatim Paragraph
- Command Paragraph
- Ordinary Block of Text
- The Intent
- Embedding Pods in Perl Modules
- Common Pod Pitfalls

- SEE ALSO
- AUTHOR

# NAME

perlpod - plain old documentation

# DESCRIPTION

A pod-to-whatever translator reads a pod file paragraph by paragraph, and translates it to the appropriate output format. There are three kinds of paragraphs: verbatim, command, and ordinary text.

## Verbatim Paragraph

A verbatim paragraph, distinguished by being indented (that is, it starts with space or tab). It should be reproduced exactly, with tabs assumed to be on 8-column boundaries. There are no special formatting escapes, so you can't italicize or anything like that. A \ means \, and nothing else.

## Command Paragraph

All command paragraphs start with ``='', followed by an identifier, followed by arbitrary text that the command can use however it pleases. Currently recognized commands are

        =head1 heading
        =head2 heading
        =item text
        =over N
        =back
        =cut
        =pod
        =for X
        =begin X
        =end X

=pod
=cut
  The ``=pod'' directive does nothing beyond telling the compiler to lay off parsing code through the next ``=cut''. It's useful for adding another paragraph to the doc if you're mixing up code and pod a lot.

=head1
=head2
  Head1 and head2 produce first and second level headings, with the text in the same paragraph as the ``=headn'' directive forming the heading description.

=over
=back
=item
  Item, over, and back require a little more explanation: ``=over'' starts a section specifically for the generation of a list using ``=item'' commands. At the end of your list, use ``=back'' to end it. You will probably want to give ``4'' as the number to ``=over'', as some formatters will use this for indentation. The unit of indentation is optional. If the unit is not given the natural indentation of the formatting system applied will be used. Note also that there are some basic rules to using =item: don't use them outside of an =over/=back block, use at least one inside an =over/=back block, you don't _have_ to include the =back if the list just runs off the document, and perhaps most importantly, keep the items consistent: either use ``=item *'' for all of them, to produce bullets, or use ``=item 1.'', ``=item 2.'', etc., to produce numbered lists, or use ``=item foo'', ``=item bar'', etc., i.e., things that looks nothing like bullets or numbers. If you start with bullets or numbers, stick with them, as many formatters use the first ``=item'' type to decide how to format the list.

=for
=begin
=end
  For, begin, and end let you include sections that are not interpreted as pod text, but passed directly to particular formatters. A formatter that can utilize that format will use the section, otherwise it will be completely ignored. The directive ``=for'' specifies that the entire next paragraph is in the format indicated by the first word after ``=for'', like this:

       =for html <br>
        <p> This is a raw HTML paragraph </p>

  The paired commands ``=begin'' and ``=end'' work very similarly to ``=for'', but instead of only accepting a single paragraph, all text from ``=begin'' to a paragraph with a matching ``=end'' are treated as a particular format.

  Here are some examples of how to use these:

       =begin html

       <br>Figure 1.<IMG SRC="figure1.png"><br>

       =end html

       =begin text

         ---------------
         |  foo        |
         |        bar  |
         ---------------

       ^^^^ Figure 1. ^^^^

       =end text

  Some format names that formatters currently are known to accept include ``roff'', ``man'', ``latex'', ``tex'', ``text'', and ``html''. (Some formatters will treat some of these as synonyms.)

  And don't forget, when using any command, that the command lasts up until the end of the paragraph, not the line. Hence in the examples below, you can see the empty lines after each command to end its paragraph.

  Some examples of lists include:

       =over 4

       =item *

       First item

       =item *

       Second item

       =back

       =over 4

       =item Foo()

       Description of Foo function

       =item Bar()

       Description of Bar function

       =back

## Ordinary Block of Text

It will be filled, and maybe even justified. Certain interior sequences are recognized both here and in commands:

        I<text>     Italicize text, used for emphasis or variables
        B<text>     Embolden text, used for switches and programs
        S<text>     Text contains non-breaking spaces
        C<code>     Render code in a typewriter font, or give some other
                    indication that this represents program text
        L<name>     A link (cross reference) to name
                        L<name>             manual page
                        L<name/ident>       item in manual page
                        L<name/"sec">       section in other manual page
                        L<"sec">            section in this manual page
                                            (the quotes are optional)
                        L</"sec">           ditto
                    same as above but only 'text' is used for output.
                    (Text can not contain the characters '/' and '|',
                    and should contain matched '<' or '>')
                        L<text|name>
                        L<text|name/ident>
                        L<text|name/"sec">
                        L<text|"sec">
                        L<text|/"sec">

        F<file>     Used for filenames
        X<index>    An index entry
        Z<>         A zero-width character
        E<escape>   A named character (very similar to HTML escapes)
                        E<lt>               A literal <
                        E<gt>               A literal >
                        E<sol>              A literal /
                        E<verbar>           A literal |
                        (these are optional except in other interior
                         sequences and when preceded by a capital letter)
                        E<n>                Character number n (probably in ASCII)
                        E<html>             Some non-numeric HTML entity, such
                                            as E<Agrave>

Most of the time, you will only need a single set of angle brackets to delimit the beginning and end of interior sequences. However, sometimes you will want to put a right angle bracket (or greater-than sign '>') inside of a sequence. This is particularly common when using a sequence to provide a different font-type for a snippet of code. As with all things in Perl, there is more than one way to do it. One way is to simply escape the closing bracket using an `E` sequence:

        C<$a E<lt>=E<gt> $b>

This will produce: ```$a <=> $b`''

A more readable, and perhaps more ``plain'' way is to use an alternate set of delimiters that doesn't require a ``>'' to be escaped. As of perl5.5.660, doubled angle brackets (``<<'' and ``>>'') may be used if and only if there is whitespace immediately following the opening delimiter and immediately preceding the closing delimiter! For example, the following will do the trick:

        C<< $a <=> $b >>

In fact, you can use as many repeated angle-brackets as you like so long as you have the same number of them in the opening and closing delimiters, and make sure that whitespace immediately follows the last '<' of the opening delimiter, and immediately precedes the first '>' of the closing delimiter. So the following will also work:

        C<<< $a <=> $b >>>
        C<<<< $a <=> $b >>>>

This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man), and any other pod2xxx and Pod::Xxxx translator that uses Pod::Parser 1.093 or later.

## The Intent

That's it. The intent is simplicity, not power. I wanted paragraphs to look like paragraphs (block format), so that they stand out visually, and so that I could run them through fmt easily to reformat them (that's F7 in my version of vi). I wanted the translator (and not me) to worry about whether `` or ' is a left quote or a right quote within filled text, and I wanted it to leave the quotes alone, dammit, in verbatim mode, so I could slurp in a working program, shift it over 4 spaces, and have it print out, er, verbatim. And presumably in a constant width font.

In particular, you can leave things like this verbatim in your text:

        Perl
        FILEHANDLE
        $variable
        function()
        manpage(3r)

Doubtless a few other commands or sequences will need to be added along the way, but I've gotten along surprisingly well with just these.

Note that I'm not at all claiming this to be sufficient for producing a book. I'm just trying to make an idiot-proof common source for nroff, TeX, and other markup languages, as used for online documentation. Translators exist for pod2man (that's for `nroff(1)` and troff(1)), pod2text, pod2html, pod2latex, and pod2fm.

## Embedding Pods in Perl Modules

You can embed pod documentation in your Perl scripts. Start your documentation with a ``=head1'' command at the beginning, and end it with a ``=cut'' command. Perl will ignore the pod text. See any of the supplied library modules for examples. If you're going to put your pods at the end of the file, and you're using an __END__ or __DATA__ cut mark, make sure to put an empty line there before the first pod directive.

        __END__

        =head1 NAME

        modern - I am a modern module

If you had not had that empty line there, then the translators wouldn't have seen it.

## Common Pod Pitfalls

- Pod translators usually will require paragraphs to be separated by completely empty lines. If you have an apparently empty line with some spaces on it, this can cause odd formatting.

- Translators will mostly add wording around a L<> link, so that `L<foo(1)>` becomes ``the foo(1) manpage'', for example (see pod2man for details). Thus, you shouldn't write things like `the LE<lt>fooE<gt> manpage`, if you want the translated document to read sensibly.

  If you need total control of the text used for a link in the output use the form L<show this text|foo> instead.

- The podchecker command is provided to check pod syntax for errors and warnings. For example, it checks for completely blank lines in pod segments and for unknown escape sequences. It is still advised to pass it through one or more translators and proofread the result, or print out the result and proofread that. Some of the problems found may be bugs in the translators, which you may or may not wish to work around.

# SEE ALSO

pod2man, PODs: Embedded Documentation in the perlsyn manpage, podchecker

# AUTHOR

Larry Wall

perlpod - plain old documentation