Pod::POM - POD Object Model
use Pod::POM;
my $parser = Pod::POM->new(\%options);
# parse from a text string
my $pom = $parser->parse_text($text)
|| die $parser->error();
# parse from a file specified by name or filehandle
my $pom = $parser->parse_text($file)
|| die $parser->error();
# parse from text or file
my $pom = $parser->parse($text_or_file)
|| die $parser->error();
# examine any warnings raised
foreach my $warning ($parser->warnings()) {
warn $warning, "\n";
}
# print table of contents using each =head1 title
foreach my $head1 ($pom->head1()) {
print $head1->title(), "\n";
}
# print each section
foreach my $head1 ($pom->head1()) {
print $head1->title(), "\n";
print $head1->content();
}
# print the entire document as HTML
use Pod::POM::View::HTML;
print Pod::POM::View::HTML->print($pom);
# create custom view
package My::View;
use base qw( Pod::POM::View::HTML );
sub view_head1 {
my ($self, $item) = @_;
return '<h1>',
$item->title->present($self),
"</h1>\n",
$item->content->present($self);
}
package main;
print My::View->print($pom);
This module implements a parser to convert Pod documents into a simple object model form known hereafter as the Pod Object Model. The object model is generated as a hierarchical tree of nodes, each of which represents a different element of the original document. The tree can be walked manually and the nodes examined, printed or otherwise manipulated. In addition, Pod::POM supports and provides view objects which can automatically traverse the tree, or section thereof, and generate an output representation in one form or another.
Let's look at a typical Pod document by way of example.
=head1 NAME
My::Module - just another My::Module
=head1 DESCRIPTION
This is My::Module, a deeply funky piece of Perl code.
=head2 METHODS
My::Module implements the following methods
=over 4
=item new(\%config)
This is the constructor method. It accepts the following
configuration options:
=over 4
=item name
The name of the thingy.
=item colour
The colour of the thingy.
=back
=item print()
This prints the thingy.
=back
=head1 AUTHOR
My::Module was written by me E<lt>me@here.orgE<gt>
This document contains 3 main sections, NAME, DESCRIPTION and
AUTHOR, each of which is delimited by an opening =head1 tag.
NAME and AUTHOR each contain only a single line of text, but
DESCRIPTION is more interesting. It contains a line of text
followed by the =head2 subsection, METHODS. This contains
a line of text and a list extending from the =over 4 to the
final =back just before the AUTHOR section starts. The list
contains 2 items, new(\%config), which itself contains some
text and a list of 2 items, and print().
Presented as plain text and using indentation to indicate the element nesting, the model then looks something like this :
NAME
My::Module - just another My::Module
DESCRIPTION
This is My::Module, a deeply funky piece of Perl code.
METHODS
My::Module implements the following methods
* new(\%config)
This is the constructor method. It accepts the
following configuration options:
* name
The name of the thingy.
* colour
The colour of the thingy.
* item print()
This prints the thingy.
AUTHOR
My::Myodule was written by me <me@here.org>
Those of you familiar with XML may prefer to think of it in the following way:
<pod>
<head1 title="NAME">
<p>My::Module - just another My::Module</p>
</head1>
<head1 title="DESCRIPTION">
<p>This is My::Module, a deeply funky piece of
Perl code.</p>
<head2 title="METHODS">
<p>My::Module implements the following methods</p>
<over indent=4>
<item title="item new(\%config)">
<p>This is the constructor method. It accepts
the following configuration options:</p>
<over indent=4>
<item title="name">
<p>The name of the thingy.</p>
</item>
<item title="colour">
<p>The colour of the thingy.</p>
</item>
</over>
</item>
<item title="print()">
<p>This prints the thingy.</p>
</item>
</over>
</head2>
</head1>
<head1 title="AUTHOR">
<p>My::Myodule was written by me <me@here.org>
</head1>
</pod>
Notice how we can make certain assumptions about various elements.
For example, we can assume that any =head1 section we find begins a
new section and implicitly ends any previous section. Similarly, we
can assume an =item ends when the next one begins, and so on. In
terms of the XML example shown above, we are saying that we're smart
enough to add a </head1> element to terminate any
previously opened <head1> when we find a new =head1 tag
in the input document.
However you like to visualise the content, it all comes down to the same underlying model. The job of the Pod::POM module is to read an input Pod document and build an object model to represent it in this structured form.
Each node in the tree (i.e. element in the document) is represented
by a Pod::POM::Node::* object. These encapsulate the attributes for
an element (such as the title for a =head1 tag) and also act as
containers for further Pod::POM::Node::* objects representing the
content of the element. Right down at the leaf nodes, we have simple
object types to represent formatted and verbatim text paragraphs and
other basic elements like these.
The Pod::POM module implements the methods parse_file($file),
parse_text($text) and parse($file_or_text) to parse Pod files and
input text. They return a Pod::POM::Node::Pod object to represent the
root of the Pod Object Model, effectively the <pod> element
in the XML tree shown above.
use Pod::POM;
my $parser = Pod::POM->new();
my $pom = $parser->parse_file($filename)
|| die $parser->error();
The parse(), parse_text() and parse_file() methods return undef on error. The error() method can be called to retrieve the error message generated. Parsing a document may also generate non-fatal warnings. These can be retrieved via the warnings() method which returns a reference to a list when called in scalar context or a list of warnings when called in list context.
foreach my $warn ($parser->warnings()) {
warn $warn, "\n";
}
Alternatively, the 'warn' configuration option can be set to have
warnings automatically raised via warn() as they are encountered.
my $parser = Pod::POM->new( warn => 1 );
Having parsed a document into an object model, we can then select various items from it. Each node implements methods (via AUTOLOAD) which correspond to the attributes and content elements permitted within in.
So to fetch the list of '=head1' sections within our parsed document, we would do the following:
my $sections = $pom->head1();
Methods like this will return a list of further Pod::POM::Node::* objects when called in list context or a reference to a list when called in scalar context. In the latter case, the list is blessed into the Pod::POM::Node::Content class which gives it certain magical properties (more on that later).
Given the list of Pod::POM::Node::Head1 objects returned by the above, we can print the title attributes of each like this:
foreach my $s (@$sections) {
print $s->title();
}
Let's look at the second section, DESCRIPTION.
my $desc = $sections->[1];
We can print the title of each subsection within it:
foreach my $ss ($desc->head2()) {
print $ss->title();
}
Hopefully you're getting the idea by now, so here's a more studly example to print the title for each item contained in the first list within the METHODS section:
foreach my $item ($desc->head2->[0]->over->[0]->item) {
print $item->title(), "\n";
}
This is all well and good if you know the precise structure of a document in advance. For those more common cases when you don't, each node that can contain other nodes provides a 'content' method to return a complete list of all the other nodes that it contains. The 'type' method can be called on any node to return its element type (e.g. 'head1', 'head2', 'over', item', etc).
foreach my $item ($pom->content()) {
my $type = $item->type();
if ($type eq 'head1') {
...
}
elsif ($type eq 'head2') {
...
}
...
}
The content for an element is represented by a reference to a list, blessed into the Pod::POM::Node::Content class. This provides some magic in the form of an overloaded stringification operator which will automatically print the contents of the list if you print the object itself. In plain English, or rather, in plain Perl, this means you can do things like the following:
foreach my $head1 ($pom->head1()) {
print '<h1>', $head1->title(), "</h1>\n\n";
print $head1->content();
}
# print all the root content
foreach my $item ($pom->content()) {
print $item;
}
# same as above
print $pom->content();
In fact, all Pod::POM::Node::* objects provide this same magic, and will attempt to Do The Right Thing to present themselves in the appropriate manner when printed. Thus, the following are all valid.
print $pom; # entire document
print $pom->content; # content of document
print $pom->head1->[0]; # just first section
print $pom->head1; # print all sections
foreach my $h1 ($pom->head1()) {
print $h1->head2(); # print all subsections
}
To understand how the different elements go about presenting themselves in "the appropriate manner", we must introduce the concept of a view. A view is quite simply a particular way of looking at the model. In real terms, we can think of a view as being some kind of output type generated by a pod2whatever converter. Notionally we can think in terms of reading in an input document, building a Pod Object Model, and then generating an HTML view of the document, and/or a LaTeX view, a plain text view, and so on.
A view is represented in this case by an object class which contains
methods for displaying each of the different element types that could
be encountered in any Pod document. There's a method for displaying
=head1 sections (view_head1()), another method for displaying
=head2 sections (view_head2()), one for =over (view_over()),
another for =item (view_item()) and so on.
If we happen to have a reference to a $node and we know it's a 'head1' node, then we can directly call the right view method to have it displayed properly:
$view = 'Pod::POM::View::HTML';
$view->view_head1($node);
Thus our earlier example can be modified to be slightly less laborious and marginally more flexible.
foreach my $node ($pom->content) {
my $type = $node->type();
if ($type eq 'head1') {
print $view->view_head1($node);
}
elsif ($type eq 'head2') {
print $view->view_head2($node);
}
...
}
However, this is still far from ideal. To make life easier, each
Pod::POM::Node::* class inherits (or possibly redefines) a
present($view) method from the Pod::POM::Node base class. This method
expects a reference to a view object passed as an argument, and it
simply calls the appropriate view_xxx() method on the view object,
passing itself back as an argument. In object parlance, this is known
as "double dispatch". The beauty of it is that you don't need to know
what kind of node you have to be able to print it. You simply pass
it a view object and leave it to work out the rest.
foreach my $node ($pom->content) {
print $node->present($view);
}
If $node is a Pod::POM::Node::Head1 object, then the view_head1($node) method gets called against the $view object. Otherwise, if it's a Pod::POM::Node::Head2 object, then the view_head2($node) method is dispatched. And so on, and so on, with each node knowing what it is and where it's going as if determined by some genetically pre-programmed instinct. Fullfilling their destinies, so to speak.
Double dispatch allows us to do away with all the explicit type checking and other nonsense and have the node objects themselves worry about where they should be routed to. At the cost of an extra method call per node, we get programmer convenience, and that's usually a Good Thing.
Let's have a look at how the view and node classes might be implemented.
package Pod::POM::View::HTML;
sub view_pod {
my ($self, $node) = @_;
return $node->content->present($self);
}
sub view_head1 {
my ($self, $node) = @_;
return "<h1>", $node->title->present($self), "</h1>\n\n"
. $node->content->present($self);
}
sub view_head2 {
my ($self, $node) = @_;
return "<h2>", $node->title->present($self), "</h2>\n\n"
. $node->content->present($self);
}
...
package Pod::POM::Node::Pod;
sub present {
my ($self, $view) = @_;
$view->view_pod($self);
}
package Pod::POM::Node::Head1;
sub present {
my ($self, $view) = @_;
$view->view_head1($self);
}
package Pod::POM::Node::Head2;
sub present {
my ($self, $view) = @_;
$view->view_head2($self);
}
...
Some of the view_xxx methods make calls back against the node objects
to display their attributes and/or content. This is shown in, for
example, the view_head1() method above, where the method prints the
section title in <h1>...<h1> tags, followed by
the remaining section content.
Note that the title() attribute is printed by calling its present() method, passing on the reference to the current view. Similarly, the content present() method is called giving it a chance to Do The Right Thing to present itself correctly via the view object.
There's a good chance that the title attribute is going to be regular text, so we might be tempted to simply print the title rather than call its present method.
sub view_head1 {
my ($self, $node) = @_;
# not recommended, prefer $node->title->present($self)
return "<h1>", $node->title(), "</h1>\n\n", ...
}
However, it is entirely valid for titles and other element attributes,
as well as regular, formatted text blocks to contain code sequences,
such like B<this> and I<this>. These are used
to indicate different markup styles, mark external references or index
items, and so on. What's more, they can be B<nested
I<indefinately>>. Pod::POM takes care of all this by
parsing such text, along with any embedded sequences, into Yet Another
Tree, the root node of which is a Pod::POM::Node::Text object,
possibly containing other Pod::POM::Node::Sequence objects. When the
text is presented, the tree is automatically walked and relevant
callbacks made against the view for the different sequence types. The
methods called against the view are all prefixed 'view_seq_', e.g.
'view_seq_bold', 'view_seq_italic'.
Now the real magic comes into effect. You can define one view to render bold/italic text in one style:
package My::View::Text;
use base qw( Pod::POM::View::Text );
sub view_seq_bold {
my ($self, $text) = @_;
return "*$text*";
}
sub view_seq_italic {
my ($self, $text) = @_;
return "_$text_";
}
And another view to render it in a different style:
package My::View::HTML;
use base qw( Pod::POM::View::HTML );
sub view_seq_bold {
my ($self, $text) = @_;
return "<b>$text</b>";
}
sub view_seq_italic {
my ($self, $text) = @_;
return "<i>$text</i>";
}
Then, you can easily view a Pod Object Model in either style:
my $text = 'My::View::Text';
my $html = 'My::View::HTML';
print $pom->present($text);
print $pom->present($html);
And you can apply this technique to any node within the object model.
print $pom->head1->[0]->present($text);
print $pom->head1->[0]->present($html);
In these examples, the view passed to the present() method has been a class name. Thus, the view_xxx methods get called as class methods, as if written:
My::View::Text->view_head1(...);
If your view needs to maintain state then you can create a view object and pass that to the present() method.
my $view = My::View->new();
$node->present($view);
In this case the view_xxx methods get called as object methods.
sub view_head1 {
my ($self, $node) = @_;
my $title = $node->title();
if ($title eq 'NAME' && ref $self) {
$self->{ title } = $title();
}
$self->SUPER::view_head1($node);
}
Whenever you print a Pod::POM::Node::* object, or do anything to cause
Perl to stringify it (such as including it another quoted string "like
$this"), then its present() method is automatically called. When
called without a view argument, the present() method uses the default
view specified in $Pod::POM::DEFAULT_VIEW, which is, by default,
'Pod::POM::View::Pod'. This view regenerates the original Pod
document, although it should be noted that the output generated may
not be exactly the same as the input. The parser is smart enough to
detect some common errors (e.g. not terminating an =over with a =back)
and correct them automatically. Thus you might find a =back
correctly placed in the output, even if you forgot to add it to the
input. Such corrections raise non-fatal warnings which can later
be examined via the warnings() method.
You can update the $Pod::POM::DEFAULT_VIEW package variable to set the default view, or call the default_view() method. The default_view() method will automatically load any package you specify. If setting the package variable directly, you should ensure that any packages required have been pre-loaded.
use My::View::HTML;
$Pod::POM::DEFAULT_VIEW = 'My::View::HTML';
or
Pod::POM->default_view('My::View::HTML');
One of the motivations for writing this module was to make it easier to customise Pod documentation to your own look and feel or local formatting conventions. By clearly separating the content (represented by the Pod Object Model) from the presentation style (represented by one or more views) it becomes much easier to achieve this.
The latest version of the Template Toolkit (2.06 at the time of writing) provides a Pod plugin to interface to this module. It also implements a new (but experimental) VIEW directive which can be used to build different presentation styles for converting Pod to other formats. The Template Toolkit is available from CPAN:
http://www.cpan.org/modules/by-module/Template/
Template Toolkit views are similar to the Pod::POM::View objects described above, except that they allow the presentation style for each Pod component to be written as a template file or block rather than an object method. The precise syntax and structure of the VIEW directive is subject to change (given that it's still experimental), but at present it can be used to define a view something like this:
[% VIEW myview %]
[% BLOCK view_head1 %]
<h1>[% item.title.present(view) %]</h1>
[% item.content.present(view) %]
[% END %]
[% BLOCK view_head2 %]
<h2>[% item.title.present(view) %]</h2>
[% item.content.present(view) %]
[% END %]
...
[% END %]
A plugin is provided to interface to the Pod::POM module:
[% USE pod %]
[% pom = pod.parse('/path/to/podfile') %]
The returned Pod Object Model instance can then be navigated and presented via the view in almost any way imaginable:
<h1>Table of Contents</h1>
<ul>
[% FOREACH section = pom.head1 %]
<li>[% section.title.present(view) %]
[% END %]
</ul>
<hr>
[% FOREACH section = pom.head1 %]
[% section.present(myview) %]
[% END %]
You can either pass a reference to the VIEW (myview) to the present() method of a Pod::POM node:
[% pom.present(myview) %] # present entire document
Or alternately call the print() method on the VIEW, passing the Pod::POM node as an argument:
[% myview.print(pom) %]
Internally, the view calls the present() method on the node, passing itself as an argument. Thus it is equivalent to the previous example.
The Pod::POM node and the view conspire to "Do The Right Thing" to process the right template block for the node. A reference to the node is available within the template as the 'item' variable.
[% BLOCK view_head2 %]
<h2>[% item.title.present(view) %]</h2>
[% item.content.present(view) %]
[% END %]
The Template Toolkit documentation contains further information on defining and using views. However, as noted above, this may be subject to change or incomplete pending further development of the VIEW directive.
Constructor method which instantiates and returns a new Pod::POM parser object.
use Pod::POM;
my $parser = Pod::POM->new();
A reference to a hash array of configuration options may be passed as an argument.
my $parser = Pod::POM->new( { warn => 1 } );
For convenience, configuration options can also be passed as a list of (key => value) pairs.
my $parser = Pod::POM->new( warn => 1 );
The following configuration options are defined:
This option can be set to have all non-Pod parts of the input document stored within the object model as 'code' elements, represented by objects of the Pod::POM::Node::Code class. It is disabled by default and code sections are ignored.
my $parser = Pod::POM->new( code => 1 );
my $podpom = $parser->parse(\*DATA);
foreach my $code ($podpom->code()) {
print "<pre>$code</pre>\n";
}
__DATA__
This is some program code.
=head1 NAME
...
This will generate the output:
<pre>This is some program code.</pre>
Note that code elements are stored within the POM element in which
they are encountered. For example, the code element below embedded
within between Pod sections is stored in the array which can be
retrieved by calling $podpom->head1->[0]->code().
=head1 NAME
My::Module::Name;
=cut
Some program code embedded in Pod.
=head1 SYNOPSIS
...
Non-fatal warnings encountered while parsing a Pod document are stored internally and subsequently available via the warnings() method.
my $parser = Pod::POM->new();
my $podpom = $parser->parse_file($filename);
foreach my $warning ($parser->warnings()) {
warn $warning, "\n";
}
The 'warn' option can be set to have warnings raised automatically
via warn() as and when they are encountered.
my $parser = Pod::POM->new( warn => 1 );
my $podpom = $parser->parse_file($filename);
If the configuration value is specified as a subroutine reference then the code will be called each time a warning is raised, passing the warning message as an argument.
sub my_warning {
my $msg = shift;
warn $msg, "\n";
};
my $parser = Pod::POM->new( warn => \&my_warning );
my $podpom = $parser->parse_file($filename);
The 'meta' option can be set to allow =meta tags within the Pod
document.
my $parser = Pod::POM->new( meta => 1 );
my $podpom = $parser->parse_file($filename);
This is an experimental feature which is not part of standard POD. For example:
=meta author Andy Wardley
These are made available as metadata items within the root node of the parsed POM.
my $author = $podpom->metadata('author');
See the METADATA section below for further information.
Parses the file specified by name or reference to a file handle. Returns a reference to a Pod::POM::Node::Pod object which represents the root node of the Pod Object Model on success. On error, undef is returned and the error message generated can be retrieved by calling error().
my $podpom = $parser->parse_file($filename)
|| die $parser->error();
my $podpom = $parser->parse_file(\*STDIN)
|| die $parser->error();
Any warnings encountered can be examined by calling the warnings() method.
foreach my $warn ($parser->warnings()) {
warn $warn, "\n";
}
Parses the Pod text string passed as an argument into a Pod Object Model, as per parse_file().
General purpose method which attempts to Do The Right Thing in calling parse_file() or parse_text() according to the argument passed.
A hash reference can be passed as an argument that contains a 'text' or 'file' key and corresponding value.
my $podpom = $parser->parse({ file => $filename })
|| die $parser->error();
Otherwise, the argument can be a reference to an input handle which is passed off to parse_file().
my $podpom = $parser->parse(\*DATA)
|| die $parser->error();
If the argument is a text string that looks like Pod text (i.e. it contains '=' at the start of any line) then it is passed to parse_text().
my $podpom = $parser->parse($podtext)
|| die $parser->error();
Otherwise it is assumed to be a filename and is passed to parse_file().
my $podpom = $parser->parse($podfile)
|| die $parser->error();
This section lists the different nodes that may be present in a Pod Object Model. These are implemented as Pod::POM::Node::* object instances (e.g. head1 => Pod::POM::Node::Head1). To present a node, a view should implement a method which corresponds to the node name prefixed by 'view_' (e.g. head1 => view_head1()).
The pod node is used to represent the root node of the Pod Object Model.
Content elements: head1, head2, head3, head4, over, begin, for, verbatim, text, code.
A head1 node contains the Pod content from a =head1 tag up to the
next =head1 tag or the end of the file.
Attributes: title
Content elements: head2, head3, head4, over, begin, for, verbatim, text, code.
A head2 node contains the Pod content from a =head2 tag up to the
next =head1 or =head2 tag or the end of the file.
Attributes: title
Content elements: head3, head4, over, begin, for, verbatim, text, code.
A head3 node contains the Pod content from a =head3 tag up to the
next =head1, =head2 or =head3 tag or the end of the file.
Attributes: title
Content elements: head4, over, begin, for, verbatim, text, code.
A head4 node contains the Pod content from a =head4 tag up to the
next =head1, =head2, =head3 or =head4 tag or the end of the file.
Attributes: title
Content elements: over, begin, for, verbatim, text, code.
The over node encloses the Pod content in a list starting at an =over
tag and continuing up to the matching =back tag. Lists may be nested
indefinately.
Attributes: indent (default: 4)
Content elements: over, item, begin, for, verbatim, text, code.
The item node encloses the Pod content in a list item starting at an
=item tag and continuing up to the next =item tag or a =back tag
which terminates the list.
Attributes: title (default: *)
Content elements: over, begin, for, verbatim, text, code.
A begin node encloses the Pod content in a conditional block starting
with a =begin tag and continuing up to the next =end tag.
Attributes: format
Content elements: verbatim, text, code.
A for node contains a single paragraph containing text relevant to a
particular format.
Attributes: format, text
A verbatim node contains a verbatim text paragraph which is prefixed by
whitespace in the source Pod document (i.e. indented).
Attributes: text
A text node contains a regular text paragraph. This may include
embedded inline sequences.
Attributes: text
A code node contains Perl code which is by default, not considered to be
part of a Pod document. The code configuration option must be set for
Pod::POM to generate code blocks, otherwise they are ignored.
Attributes: text
Embedded sequences are permitted within regular text blocks (i.e. not verbatim) and title attributes. To present these sequences, a view should implement methods corresponding to the sequence name, prefixed by 'view_seq_' (e.g. bold => view_seq_bold()).
The Pod::POM module distribution includes a number of sample view objects for rendering Pod Object Models into particular formats. These are incomplete and may require some further work, but serve at present to illustrate the principal and can be used as the basis for your own view objects.
A script is provided for converting Pod documents to other format by
using the view objects provided. The pom2 script should be called
with two arguments, the first specifying the output format, the second
the input filename. e.g.
$ pom2 text My/Module.pm > README
$ pom2 html My/Module.pm > ~/public_html/My/Module.html
You can also create symbolic links to the script if you prefer and leave it to determine the output format from its own name.
$ ln -s pom2 pom2text
$ ln -s pom2 pom2html
$ pom2text My/Module.pm > README
$ pom2html My/Module.pm > ~/public_html/My/Module.html
The distribution also contains a trivial script, podlint
(previously pomcheck), which checks a Pod document for
well-formedness by simply parsing it into a Pod Object Model with
warnings enabled. Warnings are printed to STDERR.
$ podlint My/Module.pm
The -f option can be set to have the script attempt to fix any problems
it encounters. The regenerated Pod output is printed to STDOUT.
$ podlint -f My/Module.pm > newfile
This module includes support for an experimental new =meta tag. This
is disabled by default but can be enabled by loading Pod::POM with the
meta option.
use Pod::POM qw( meta );
Alternately, you can specify the meta option to be any true value when
you instantiate a Pod::POM parser:
my $parser = Pod::POM->new( meta => 1 );
my $pom = $parser->parse_file($filename);
Any =meta tags in the document will be stored as metadata items in the
root node of the Pod model created.
For example:
=meta module Foo::Bar
=meta author Andy Wardley
You can then access these items via the metadata() method.
print "module: ", $pom->metadata('module'), "\n";
print "author: ", $pom->metadata('author'), "\n";
or
my $metadata = $pom->metadata();
print "module: $metadata->{ module }\n";
print "author: $metadata->{ author }\n";
Please note that this is an experimental feature which is not supported by other POD processors and is therefore likely to be most incompatible. Use carefully.
Andy Wardley <abw@kfs.org>
This is version 0.15 of the Pod::POM module.
Copyright (C) 2000-2002 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
For the definitive reference on Pod, see perlpod.
For an overview of Pod::POM internals and details relating to subclassing of POM nodes, see Pod::POM::Node.
There are numerous other fine Pod modules available from CPAN which perform conversion from Pod to other formats. In many cases these are likely to be faster and quite possibly more reliable and/or complete than this module. But as far as I know, there aren't any that offer the same kind of flexibility in being able to customise the generated output. But don't take my word for it - see your local CPAN site for further details:
http://www.cpan.org/modules/by-module/Pod/