NAME

perlpod - the Plain Old Documentation format

DESCRIPTION

Pod is a simple-to-use markup language used for writing documentation for Perl,
Perl programs, and Perl modules.

Translators are available for converting Pod to various formats like plain
text, HTML, man pages, and more.

Pod markup consists of three basic kinds of paragraphs: [ilink] ordinary, 
[ilink] verbatim, and [ilink] command.

Ordinary Paragraph

Most paragraphs in your documentation will be ordinary blocks of text, like
this one. You can simply type in your text without any markup whatsoever, and
with just a blank line before and after. When it gets formatted, it will
undergo minimal formatting, like being rewrapped, probably put into a
proportionally spaced font, and maybe even justified.

You can use formatting codes in ordinary paragraphs, for bold, italic,
code-style, perlfaq?, and more. Such codes are explained in the "[ilink] 
Formatting Codes" section, below.

Verbatim Paragraph

Verbatim paragraphs are usually used for presenting a codeblock or other text
which does not require any special parsing or formatting, and which shouldn't
be wrapped.

A verbatim paragraph is distinguished by having its first character be a space
or a tab. (And commonly, all its lines begin with spaces and/or tabs.) It
should be reproduced exactly, with tabs assumed to be on 8-column boundaries.
There are no special formatting codes, so you can't italicize or anything like
that. A \ means \, and nothing else.

Command Paragraph

A command paragraph is used for special treatment of whole chunks of text,
usually as headings or parts of lists.

All command paragraphs (which are typically only one line long) start with "=",
followed by an identifier, followed by arbitrary text that the command can use
however it pleases. Currently recognized commands are

    =head1 Heading Text
    =head2 Heading Text
    =head3 Heading Text
    =head4 Heading Text
    =over indentlevel
    =item stuff
    =back
    =cut
    =pod
    =begin format
    =end format
    =for format text... 

To explain them each in detail:

=head1 Heading Text
=head2 Heading Text
=head3 Heading Text
=head4 Heading Text
   
    Head1 through head4 produce headings, head1 being the highest level. The
    text in the rest of this paragraph is the content of the heading. For
    example:
   
      =head2 Object Attributes 
   
    The text "Object Attributes" comprises the heading there. (Note that head3
    and head4 are recent additions, not supported in older Pod translators.)
    The text in these heading commands can use formatting codes, as seen here:
   
      =head2 Possible Values for C<$/> 
   
    Such commands are explained in the "[ilink] Formatting Codes" section,
    below.
   
=over indentlevel
=item stuff...
=back
   
    Item, over, and back require a little more explanation: "=over" starts a
    region specifically for the generation of a list using "=item" commands, or
    for indenting (groups of) normal paragraphs. At the end of your list, use "
    =back" to end it. The indentlevel option to "=over" indicates how far over
    to indent, generally in ems (where one em is the width of an "M" in the
    document's base font) or roughly comparable units; if there is no
    indentlevel option, it defaults to four. (And some formatters may just
    ignore whatever indentlevel you provide.) In the stuff in =item stuff...,
    you may use formatting codes, as seen here:
   
      =item Using C<$|> to Control Buffering 
   
    Such commands are explained in the "[ilink] Formatting Codes" section,
    below.
   
    Note also that there are some basic rules to using "=over" ... "=back"
    regions:
   
      + Don't use "=item"s outside of an "=over" ... "=back" region.
       
      + The first thing after the "=over" command should be an "=item", unless
        there aren't going to be any items at all in this "=over" ... "=back"
        region.
       
      + Don't put "=headn" commands inside an "=over" ... "=back" region.
       
      + 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. -- namely, things that look nothing like bullets or numbers.
       
        If you start with bullets or numbers, stick with them, as formatters
        use the first "=item" type to decide how to format the list.
       
=cut
   
    To end a Pod block, use a blank line, then a line beginning with "=cut",
    and a blank line after it. This lets Perl (and the Pod formatter) know that
    this is where Perl code is resuming. (The blank line before the "=cut" is
    not technically necessary, but many older Pod processors require it.)
   
=pod
   
    The "=pod" command by itself doesn't do much of anything, but it signals to
    Perl (and Pod formatters) that a Pod block starts here. A Pod block starts
    with any command paragraph, so a "=pod" command is usually used just when
    you want to start a Pod block with an ordinary paragraph or a verbatim
    paragraph. For example:
   
      =item stuff() 
      This function does stuff. 
      =cut 
      sub stuff {
        ...
      } 
      =pod 
      Remember to check its return value, as in: 
        stuff() || die "Couldn't do stuff!"; 
      =cut 
=begin formatname
=end formatname
=for formatname text...
   
    For, begin, and end will let you have regions of text/code/data that are
    not generally interpreted as normal Pod text, but are passed directly to
    particular formatters, or are otherwise special. A formatter that can use
    that format will use the region, otherwise it will be completely ignored.
   
    A command "=begin formatname", some paragraphs, and a command "=end
    formatname", mean that the text/data inbetween is meant for formatters that
    understand the special format called formatname. For example,
   
      =begin html 
      
    ---------------------------------------------------------------------------
     [thang]
      
    
     This is a raw HTML paragraph 
    
    
     
      =end html 
   
    The command "=for formatname text..." specifies that the remainder of just
    this paragraph (starting right after formatname) is in that special format.
   
      =for html 
    ---------------------------------------------------------------------------
     [thang]
      
    
     This is a raw HTML paragraph 
    
    
     
   
    This means the same thing as the above "=begin html" ... "=end html"
    region.
   
    That is, with "=for", you can have only one paragraph's worth of text
    (i.e., the text in "=foo targetname text..."), but with "=begin targetname"
    ... "=end targetname", you can have any amount of stuff inbetween. (Note
    that there still must be a blank line after the "=begin" command and a
    blank line before the "=end" command.
   
    Here are some examples of how to use these:
   
      =begin html 
      
    Figure 1.
    [figure1]
     
      =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.)
   
    A format name of "comment" is common for just making notes (presumably to
    yourself) that won't appear in any formatted version of the Pod document:
   
      =for comment
      Make sure that all the available options are documented! 
   
    Some formatnames will require a leading colon (as in "=for :formatname", or
    "=begin :formatname" ... "=end :formatname"), to signal that the text is
    not raw data, but instead is Pod text (i.e., possibly containing formatting
    codes) that's just not for normal formatting (e.g., may not be a normal-use
    paragraph, but might be for formatting as a footnote).
   
And don't forget, when using any command, that the command lasts up until the
end of its paragraph, not its line. So in the examples below, you can see that
every command needs the blank line after it, to end its paragraph.

Some examples of lists include:

  =over 
  =item * 
  First item 
  =item * 
  Second item 
  =back 
  =over 
  =item Foo() 
  Description of Foo function 
  =item Bar() 
  Description of Bar function 
  =back 

Formatting Codes

In ordinary paragraphs and in some command paragraphs, various formatting codes
(a.k.a. "interior sequences") can be used:

I -- italic text
   
    Used for emphasis ("be I") and parameters ("redo I")
   
B -- bold text
   
    Used for switches ("perl's B<-n> switch"), programs ("some systems provide
    a B for that"), emphasis ("be B"), and so on ("and that feature is known as
    B").
   
C -- code text
   
    Renders code in a typewriter font, or gives some other indication that this
    represents program text ("C") or some other form of computerese ("C").
   
L -- a hyperlink
   
    There are various syntaxes, listed below. In the syntaxes given, text,
    name, and section cannot contain the characters '/' and '|'; and any '<' or
    '>' should be matched.
   
      + L
       
        Link to a Perl manual page (e.g., L). Note that name should not contain
        spaces. This syntax is also occasionally used for references to UNIX
        man pages, as in L.
       
      + L or L
       
        Link to a section in other manual page. E.g., L
       
      + L or L or L<"sec">
       
        Link to a section in this manual page. E.g., L
       
    A section is started by the named heading or item. For example, L or L both
    link to the section started by "=item $." in perlvar. And L or L both link
    to the section started by "=head2 For Loops" in perlsyn.
   
    To control what text is used for display, you use "L", as in:
   
      + L
       
        Link this text to that manual page. E.g., L
       
      + L or L
       
        Link this text to that section in that manual page. E.g., L
       
      + L or L or L
       
        Link this text to that section in this manual page. E.g., L
       
    Or you can link to a web page:
   
      + L
       
        Links to an absolute URL. For example, L. But note that there is no
        corresponding L syntax, for various reasons.
       
E -- a character escape
   
    Very similar to HTML/XML &foo; "entity references":
   
      + E -- a literal < (less than)
       
      + E -- a literal > (greater than)
       
      + E -- a literal | (vertical bar)
       
      + E = a literal / (solidus)
       
        The above four are optional except in other formatting codes, notably L
        <...>, and when preceded by a capital letter.
       
      + E
       
        Some non-numeric HTML entity name, such as E, meaning the same thing as
         in HTML -- i.e., a lowercase e with an acute (/-shaped) accent.
       
      + E
       
        The ASCII/Latin-1/Unicode character with that number. A leading "0x"
        means that number is hex, as in E<0x201E>. A leading "0" means that
        number is octal, as in E<075>. Otherwise number is interpreted as being
        in decimal, as in E<181>.
       
        Note that older Pod formatters might not recognize octal or hex numeric
        escapes, and that many formatters cannot reliably render characters
        above 255. (Some formatters may even have to use compromised renderings
        of Latin-1 characters, like rendering E as just a plain "e".)
       
F -- used for filenames
   
    Typically displayed in italics. Example: "F<.cshrc>"
   
S -- text contains non-breaking spaces
   
    This means that the words in text should not be broken across lines.
    Example: S<$x ? $y : $z>.
   
X -- an index entry
   
    This is ignored by most formatters, but some may use it for building
    indexes. It always renders as empty-string. Example: X
   
Z<> -- a null (zero-effect) formatting code
   
    This is rarely used. It's one way to get around using an E<...> code
    sometimes. For example, instead of "NE3" (for "N<3") you could write "NZ<>
    <3" (the "Z<>" breaks up the "N" and the "<" so they can't be considered
    the part of a (fictitious) "N<...>" code.
   
Most of the time, you will need only a single set of angle brackets to delimit
the beginning and end of formatting codes. However, sometimes you will want to
put a real right angle bracket (a greater-than sign, '>') inside of a
formatting code. This is particularly common when using a formatting code 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 code:

    C<$a E=E $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 single ">" to be escaped. With the Pod
formatters that are standard starting with perl5.5.660, doubled angle brackets
("<<" and ">>") may be used if and only if there is whitespace right after the
opening delimiter and whitespace right before 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. (The
whitespace is ignored.) So the following will also work:

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

And they all mean exactly the same as this:

    C<$a E=E $b> 

As a further example, this means that if you wanted to put these bits of code
in C (code) style:

    open(X, ">>thing.dat") || die $!
    $foo->bar(); 

you could do it like so:

    C<<< open(X, ">>thing.dat") || die $! >>>
    C<< $foo->bar(); >> 

which is presumably easier to read than the old way:

    CEthing.dat") || die $!>
    C<$foo-Ebar(); >> 

This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man), and
any other pod2xxx or Pod::Xxxx translators that use Pod::Parser 1.093 or later,
or Pod::Tree 1.02 or later.

The Intent

The intent is simplicity of use, not power of expression. Paragraphs 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, or
Esc Q in my version of emacs). I wanted the translator to always leave the '
and ` and " quotes alone, in verbatim mode, so I could slurp in a working
program, shift it over four spaces, and have it print out, er, verbatim. And
presumably in a monospace font.

The Pod format is not necessarily sufficient for writing a book. Pod is just
meant to be an idiot-proof common source for nroff, HTML, TeX, and other markup
languages, as used for online documentation. Translators exist for pod2text, 
pod2html, pod2man (that's for nroff(1) and troff(1)), pod2latex, and pod2fm.
Various others are available in CPAN.

Embedding Pods in Perl Modules

You can embed Pod documentation in your Perl modules and scripts. Start your
documentation with an empty line, a "=head1" command at the beginning, and end
it with a "=cut" command and an empty line. Perl will ignore the Pod text. See
any of the supplied library modules for examples. If you're going to put your
Pod 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 command.

  __END__ 
  =head1 NAME 
  Time::Local - efficiently compute time from local and GMT time 

Without that empty line before the "=head1", many translators wouldn't have
recognized the "=head1" as starting a Pod block.

Hints for Writing Pod

  * The podchecker command is provided for checking Pod syntax for errors and
    warnings. For example, it checks for completely blank lines in Pod blocks
    and for unknown commands and formatting codes. You should still also pass
    your document 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.
   
  * If you're more familiar with writing in HTML than with writing in Pod, you
    can try your hand at writing documentation in simple HTML, and converting
    it to Pod with the experimental Pod::HTML2Pod? module, (available in CPAN),
    and looking at the resulting code. The experimental Pod::PXML? module in
    CPAN might also be useful.
   
  * Many older Pod translators require the lines before every Pod command and
    after every Pod command (including "=cut"!) to be a blank line. Having
    something like this:
   
     # - - - - - - - - - - - -
     =item $firecracker->boom() 
     This noisily detonates the firecracker object.
     =cut
     sub boom {
     ... 
   
    ...will make such Pod translators completely fail to see the Pod block at
    all.
   
    Instead, have it like this:
   
     # - - - - - - - - - - - - 
     =item $firecracker->boom() 
     This noisily detonates the firecracker object. 
     =cut 
     sub boom {
     ... 
  * Some older Pod translators require paragraphs (including command paragraphs
    like "=head2 Functions") to be separated by completely empty lines. If you
    have an apparently empty line with some spaces on it, this might not count
    as a separator for those translators, and that could cause odd formatting.
   
  * Older translators might add wording around an L<> link, so that L may
    become "the Foo::Bar manpage", for example. So you shouldn't write things
    like the L documentation, if you want the translated document to read
    sensibly -- instead write the L documentation or L, to control how the link
    comes out.
   
  * Going past the 70th column in a verbatim block might be ungracefully
    wrapped by some formatters.
   
SEE ALSO

perlpodspec?, perlsyn?, perlnewmod?, perldoc?, pod2html?, pod2man?, podchecker?
.

AUTHOR

Larry Wall, Sean M. Burke

