#Time-stamp: "2001-05-25 21:29:02 MDT"

=head1 NAME

Pod::PXML -- pxml2pod, pod2pxml

=head1 SYNOPSIS

  use Pod::PXML;
  
  # Take from a file...
  open(XMLOUT, ">foo.xml") || die "can't wropen foo.xml: $!";
  binmode(XMLOUT);
  print XMLOUT Pod::PXML::pod2xml('foo.pod');
  close(XMLOUT);
  
  # Take from a file, going the other way:
  open(PODOUT, ">foo.pod") || die "can't wropen foo.pod: $!";
  binmode(PODOUT);
  print PODOUT Pod::PXML::xml2pod('foo.xml');
  close(PODOUT);
  
  # Or take from STDIN:
  print '', Pod::PXML::pod2xml(\join '', <STDIN>);
  # Or the other way;
  print '', Pod::PXML::xml2pod(\join '', <STDIN>);

=head1 DESCRIPTION

Perl's documention is conventionally expressed in
Plain Old Documentation.

POD-format is a wonderfully concise text format, but it is quite
idiosyncratic.  This module seeks to make it easier to turn
text that's in POD-format into XML, and to turn text that's in
XML into POD-format.

=head1 WARNING

This module is experimental!!  It works right on almost all data,
but there are a few oddities left -- mostly in the handling of odd
LE<lt>...E<gt> syntax.  Some of these are because of bugs in
the current Pod::Tree version (1.06), and some of these are because
of basic conceptual problems in perlpod.  Both of these should
be cleared up eventually.  If you get strange results from this
module, do email me.

=head1 FUNCTIONS

=over

TODO: document options?

TODO: allow treating comment blocks outside paragrapms as <!-- ... -->?

=item $xml_text = Pod::PXML::pod2xml($filename);

=item $xml_text = Pod::PXML::pod2xml(\$content);

Returns XML content that represents the POD-format text that was input.

=item $pod_text = Pod::PXML::xml2pod($filename);

=item $pod_text = Pod::PXML::xml2pod(\$content);

Returns POD-format content that represents the PXML text that was input.

=back

=head1 WARNING

This module and the PXML DTD are still in the EXPERIMENTAL stage.
If you don't like the way something works, or if you think something's
broken, email me sooner rather than later!
I mean for this module to be actually useful to people in their
XMLificational PODulatory document doings.

=head1 ABOUT THE XML DOCUMENT TYPE

This module's idea of XML isn't just I<any> sort of XML, but is XML
complying to a DTD.  "PXML" is what I call the document type
that my DTD declares.

The design goals of PXML are to be a 1:1 representation of all I<meaningful
distinctions> you can make in valid POD-format -- if it's a meaningful
distinction you can validly express in POD-format, I want to be able to convert
that to isomorphic PXML.  Moreover, I want to be able to write
PXML that can represent any meaningful distinction in valid POD-format,
once I convert it to POD-format.

So, whether you write "$aE<gt>$b" in POD-format as "$aEE<lt>ltE<gt>$b"
or as "$aEE<lt>60E<gt>$b" is I<not> a meaningful distinction, because
"EE<lt>ltE<gt>" or as "EE<lt>60E<gt>" represent the same character.
However, the difference between "=head1" and "=head2" is meaningful,
and the difference between "CE<lt>...E<gt>" and "FE<lt>...E<gt>" is
meaningful, and so these distinctions should be present in the PXML
representation of the POD.

A secondary design goal is that PXML be as minimal as possible; specifically,
there shouldn't be anything in PXML (whether element or attribute)
that doesn't correspond I<directly> to some part of POD-format.

So, while you might want to represent this:

  =item Foo
  
  Bar

as this:

  <item>
    <label>Foo</label>
    <p>Bar</p>
  </item>

or while you might want to represent this:

  =head1 Foo
  
  Bar

as this:

  <section1>
    <head1>Foo</head1>
    <p>Bar</p>
  </section1>

...those are  I<not> the way
I do it, even tho I considered both.  Why did I decide against
those?  Because there's no "label" or "section1" in POD-format.

Instead, I do:

  <item>Foo</item>
  <p>Bar</p>

and

  <head1>Foo</item>
  <p>Bar</p>
  
Moreover:

=over

For any valid POD-format input you provide, this module should emit XML
that conforms to the PXML DTD.  For any XML input that you feed in that
comforms to the PXML DTD, this module should emit valid POD.

=back

=head2 POD-format / PXML Correspondences

The PXML DTD is still not entirely nailed down, but once it is, then
this section should be rather more verbose.

  POD-format  -------------------------------  PXML

  A normal paragraph:
  Hummina hummina?                  =    <p>Hummina hummina?
  Woozle wuzzle.                         Woozle wuzzle.</p>

--

  A verbatim paragraph:             =    <pre>
    while(1) {                             while(1) {
      print "Matanga!!\n";                   print "Matanga!!\n";
    }                                      }
                                         </pre>

--

  =head1 DEMANDS
                                    =    <head1>DEMANDS</head1>
  My list of demands:                    <p>My list of demands:</p>

(ditto for head2, head3, head4)

--

  =over 5
                                         <list indent="5">
  =item 1.                          =    <item>1.</item>
                                         <p>I like pie.</p>
  I want pie.                            </list>
  
  =back

--

  Mmmmmmm.                               <p>Mmmmmmm.
  Glorious I<italic pie>,                Glorious <i>italic pie</i>,
  C<codic pie>, F<filed pie>,       =    <c>codic pie</c>, <f>filed pie</f>,
  B<boldened pie>, and even              <b>boldened pie</b>, and even
  even X<indexed pie>.                   even <x>indexed pie</x>.</p>
  
  And even S<nested unbroken        =    And even <s>nested unbroken
  I<italic B<boldened                    <i>italic <b>boldened
  C<codic pie>>>>!                       <c>codic pie</c></b></i></s>!
  
  See also L<rhubarb pie            =    <link page="Pie::Filling"
  filling|Pie::Filling/"Rhubarb">.       section="Rhubarb"
                                         >rhubarb pie filling</link>

(Formatting of LE<lt>...E<gt> elements where there's no
LE<lt>text|...E<gt> is inconsistent across different POD
renderers.  I strongly advise that you always use
the LE<lt>text|...E<gt> style.)

If you're unsure about a particular POD-format construct, run pod2pxml
on it, and see what happens.  Be sure to report any oddities to me.

Note that XML PIs and comments are currently ignored by translation
to POD.  If you want comments that survive round-tripping pxml2pod2pxml,
then you'd probably better put them in a

  <for target="comments">Comments Here</for>

block.  And remember that those can't occur in the middle of
paragraphs.

=head1 TODO

There should be a Pod::Tree/Pod::Parser subclass that will deal
with:

  =begin pxml
  
  [...pxml...]
  
  =end pxml

and parse it as if it were POD-format, transparently.

Conversely, there should be improved facility for
reading POD-format transparently as PXML.

Smarter support for EE<lt>...E<gt> in pxml2pod -- currently
most high-bit characters just end up as EE<lt>numberE<gt>.

Make the XML output indented?

(Optionally?) Collapse non-verbatim whitespace in
pxml2pod?  Also (optionally?) re-wrap?

Handling of XML namespaces?  At least for skipping foreign-namespace
elements?  Tell me what you want.

Handling of different encodings?  Allow specifying UTF-8 / Latin-1
POD to/from UTF-8 / Latin-1 PXML?

=head1 SEE ALSO

L<perlpod|perlpod> documents POD-format.

L<Pod::Tree|Pod::Tree> is the class that I use for parsing POD-format.

L<XML::Parser|XML::Parser> is the class that I use for parsing XML.

L<Pod::Parser|Pod::Parser> is a different POD-format parser class.

L<Pod::XML|Pod::XML> is Matt Sergeant's approach to this, and it
has a quite different doctype.

I once wrote L<Pod::HTML2POD|Pod::HTML2POD>, which is much much
crazier inside than this module is.  After I while, I figure that
if I could (effectively!) convert HTML into POD, why not XML?
And seeing Matt Sergeant's Pod::XML module got me going.

=head1 COPYRIGHT AND DISCLAIMER

Copyright (c) 2001 Sean M. Burke.  All rights reserved.

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

This program is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of
merchantability or fitness for a particular purpose.

=head1 AUTHOR

Sean M. Burke, sburke@cpan.org

=cut

# "If the funk ain't broke, 'en don't try to fix it!" -- Bootsy Collins