subclassing.pod

source of perl for linux application,

    </item-bullet>
  </over-bullet>

=item events with an element_name of over-number

When an "=over ... Z<>=back" block is parsed where the items are
a numbered list, it will produce this event structure:

  <over-number indent="4" start_line="543">
    <item-number number="1" start_line="545">
      ...Stuff...
    </item-number>
    ...more item-number...
  </over-bullet>

This is like the "over-bullet" event structure; but note that the contents
are "item-number" instead of "item-bullet", and note that they will have
a "number" attribute, which some formatters/processors may ignore
(since, for example, there's no need for it in HTML when producing
an "<UL><LI>...</LI>...</UL>" structure), but which any processor may use.

Note that the values for the I<number> attributes of "item-number"
elements in a given "over-number" area I<will> start at 1 and go up by
one each time.  If the Pod source doesn't follow that order (even though
it really should should!), whatever numbers it has will be ignored (with
the correct values being put in the I<number> attributes), and an error
message might be issued to the user.

=item events with an element_name of over-text

These events are are somewhat unlike the other over-*
structures, as far as what their contents are.  When
an "=over ... Z<>=back" block is parsed where the items are
a list of text "subheadings", it will produce this event structure:

  <over-text indent="4" start_line="543">
    <item-text>
      ...stuff...
    </item-text>
    ...stuff (generally Para or Verbatim elements)...
    <item-text>
    ...more item-text and/or stuff...
  </over-text>

The I<indent> attribute is as with the other over-* events.

For example, this Pod source:

  =over
  
  =item Foo
  
  Stuff
  
  =item Bar I<baz>!
  
  Quux
  
  =back

produces this event structure:

  <over-text indent="4" start_line="20">
    <item-text start_line="22">
      Foo
    </item-text>
    <Para start_line="24">
      Stuff
    </Para>
    <item-text start_line="26">
      Bar
        <I>
          baz
        </I>
      !
    </item-text>
    <Para start_line="28">
      Quux
    </Para>
  </over-text>



=item events with an element_name of over-block

These events are are somewhat unlike the other over-*
structures, as far as what their contents are.  When
an "=over ... Z<>=back" block is parsed where there are no items,
it will produce this event structure:

  <over-block indent="4" start_line="543">
    ...stuff (generally Para or Verbatim elements)...
  </over-block>

The I<indent> attribute is as with the other over-* events.

For example, this Pod source:

  =over
  
  For cutting off our trade with all parts of the world
  
  For transporting us beyond seas to be tried for pretended offenses
  
  He is at this time transporting large armies of foreign mercenaries to
  complete the works of death, desolation and tyranny, already begun with
  circumstances of cruelty and perfidy scarcely paralleled in the most
  barbarous ages, and totally unworthy the head of a civilized nation.
  
  =cut
  
will produce this event structure:

  <over-block indent="4" start_line="2">
    <Para start_line="4">
      For cutting off our trade with all parts of the world
    </Para>
    <Para start_line="6">
      For transporting us beyond seas to be tried for pretended offenses
    </Para>
    <Para start_line="8">
      He is at this time transporting large armies of [...more text...]
    </Para>
  </over-block>

=item events with an element_name of item-bullet

See L</"events with an element_name of over-bullet">, above.

=item events with an element_name of item-number

See L</"events with an element_name of over-number">, above.

=item events with an element_name of item-text

See L</"events with an element_name of over-text">, above.

=item events with an element_name of for

TODO...

=item events with an element_name of Data

TODO...

=back



=head1 More Pod::Simple Methods

Pod::Simple provides a lot of methods that aren't generally interesting
to the end user of an existing Pod formatter, but some of which you
might find useful in writing a Pod formatter. They are listed below. The
first several methods (the accept_* methods) are for declaring the
capabilites of your parser, notably what C<=for I<targetname>> sections
it's interested in, what extra NE<lt>...E<gt> codes it accepts beyond
the ones described in the I<perlpod>.

=over

=item C<< $parser->accept_targets( I<SOMEVALUE> ) >>

As the parser sees sections like:

    =for html  <img src="fig1.jpg">

or

    =begin html

      <img src="fig1.jpg">

    =end html

...the parser will ignore these sections unless your subclass has
specified that it wants to see sections targetted to "html" (or whatever
the formatter name is).

If you want to process all sections, even if they're not targetted for you,
call this before you start parsing:

  $parser->accept_targets('*');

=item C<< $parser->accept_targets_as_text(  I<SOMEVALUE>  ) >>

This is like accept_targets, except that it specifies also that the
content of sections for this target should be treated as Pod text even
if the target name in "=for I<targetname>" doesn't start with a ":".

At time of writing, I don't think you'll need to use this.


=item C<< $parser->accept_codes( I<Codename>, I<Codename>...  ) >>

This tells the parser that you accept additional formatting codes,
beyond just the standard ones (I B C L F S X, plus the two weird ones
you don't actually see in the parse tree, Z and E). For example, to also
accept codes "N", "R", and "W":

    $parser->accept_codes( qw( N R W ) );

B<TODO: document how this interacts with =extend, and long element names>


=item C<< $parser->accept_directive_as_data( I<directive_name> ) >>

=item C<< $parser->accept_directive_as_verbatim( I<directive_name> ) >>

=item C<< $parser->accept_directive_as_processed( I<directive_name> ) >>

In the unlikely situation that you need to tell the parser that you will
accept additional directives ("=foo" things), you need to first set the
parset to treat its content as data (i.e., not really processed at
all), or as verbatim (mostly just expanding tabs), or as processed text
(parsing formatting codes like BE<lt>...E<gt>).

For example, to accept a new directive "=method", you'd presumably
use:

    $parser->accept_directive_as_processed("method");

so that you could have Pod lines like:

    =method I<$whatever> thing B<um>

Making up your own directives breaks compatibility with other Pod
formatters, in a way that using "=for I<target> ..." lines doesn't;
however, you may find this useful if you're making a Pod superset
format where you don't need to worry about compatibility.


=item C<< $parser->nbsp_for_S( I<BOOLEAN> ); >>

Setting this attribute to a true value (and by default it is false) will
turn "SE<lt>...E<gt>" sequences into sequences of words separated by
C<\xA0> (non-breaking space) characters. For example, it will take this:

    I like S<Dutch apple pie>, don't you?

and treat it as if it were:

    I like DutchE<nbsp>appleE<nbsp>pie, don't you?

This is handy for output formats that don't have anything quite like an
"SE<lt>...E<gt>" code, but which do have a code for non-breaking space.

There is currently no method for going the other way; but I can
probably provide one upon request.


=item C<< $parser->version_report() >>

This returns a string reporting the $VERSION value from your module (and
its classname) as well as the $VERSION value of Pod::Simple.  Note that
L<perlpodspec> requires output formats (wherever possible) to note
this detail in a comment in the output format.  For example, for
some kind of SGML output format:

    print OUT "<!-- \n", $parser->version_report, "\n -->";


=item C<< $parser->pod_para_count() >>

This returns the count of Pod paragraphs seen so far.


=item C<< $parser->line_count() >>

This is the current line number being parsed. But you might find the
"line_number" event attribute more accurate, when it is present.


=item C<< $parser->nix_X_codes(  I<SOMEVALUE>  ) >>

This attribute, when set to a true value (and it is false by default)
ignores any "XE<lt>...E<gt>" sequences in the document being parsed.
Many formats don't actually use the content of these codes, so have
no reason to process them.


=item C<< $parser->merge_text(  I<SOMEVALUE>  ) >>

This attribute, when set to a true value (and it is false by default)
makes sure that only one event (or token, or node) will be created
for any single contiguous sequence of text.  For example, consider
this somewhat contrived example:

    I just LOVE Z<>hotE<32>apple pie!

When that is parsed and events are about to be called on it, it may
actually seem to be four different text events, one right after another:
one event for "I just LOVE ", one for "hot", one for " ", and one for
"apple pie!". But if you have merge_text on, then you're guaranteed
that it will be fired as one text event:  "I just LOVE hot apple pie!".


=item C<< $parser->code_handler(  I<CODE_REF>  ) >>

This specifies code that should be called when a code line is seen
(i.e., a line outside of the Pod).  Normally this is undef, meaning
that no code should be called.  If you provide a routine, it should
start out like this:

    sub get_code_line {  # or whatever you'll call it
      my($line, $line_number, $parser) = @_;
      ...
    }

Note, however, that sometimes the Pod events aren't processed in exactly
the same order as the code lines are -- i.e., if you have a file with
Pod, then code, then more Pod, sometimes the code will be processed (via
whatever you have code_handler call) before the all of the preceding Pod
has been processed.


=item C<< $parser->cut_handler(  I<CODE_REF>  ) >>

This is just like the code_handler attribute, except that it's for
"=cut" lines, not code lines. The same caveats apply. "=cut" lines are
unlikely to be interesting, but this is included for completeness.


=item C<< $parser->whine( I<linenumber>, I<complaint string> ) >>

This notes a problem in the Pod, which will be reported to in the "Pod
Errors" section of the document and/or send to STDERR, depending on the
values of the attributes C<no_whining>, C<no_errata_section>, and
C<complain_stderr>.

=item C<< $parser->scream( I<linenumber>, I<complaint string> ) >>

This notes an error like C<whine> does, except that it is not
suppressable with C<no_whining>. This should be used only for very
serious errors.


=item C<< $parser->source_dead(1) >>

This aborts parsing of the current document, by switching on the flag
that indicates that EOF has been seen.  In particularly drastic cases,
you might want to do this.  It's rather nicer than just calling
C<die>!

=item C<< $parser->hide_line_numbers( I<SOMEVALUE> ) >>

Some subclasses that indescriminately dump event attributes (well,
except for ones beginning with "~") can use this object attribute for
refraining to dump the "start_line" attribute.

=item C<< $parser->no_whining( I<SOMEVALUE> ) >>

This attribute, if set to true, will suppress reports of non-fatal
error messages.  The default value is false, meaning that complaints
I<are> reported.  How they get reported depends on the values of
the attributes C<no_errata_section> and C<complain_stderr>.

=item C<< $parser->no_errata_section( I<SOMEVALUE> ) >>

This attribute, if set to true, will suppress generation of an errata
section.  The default value is false -- i.e., an errata section will be
generated.

=item C<< $parser->complain_stderr( I<SOMEVALUE> ) >>

This attribute, if set to true will send complaints to STDERR.  The
default value is false -- i.e., complaints do not go to STDERR.

=item C<< $parser->bare_output( I<SOMEVALUE> ) >>

Some formatter subclasses use this as a flag for whether output should
have prologue and epilogue code omitted. For example, setting this to
true for an HTML formatter class should omit the
"<html><head><title>...</title><body>..." prologue and the
"</body></html>" epilogue.

If you want to set this to true, you should probably also set
C<no_whining> or at least C<no_errata_section> to true.

=item C<< $parser->preserve_whitespace( I<SOMEVALUE> ) >>

If you set this attribute to a true value, the parser will try to
preserve whitespace in the output.  This means that such formatting
conventions as two spaces after periods will be preserved by the parser.
This is primarily useful for output formats that treat whitespace as
significant (such as text or *roff, but not HTML).

=back


=head1 SEE ALSO

L<Pod::Simple> -- event-based Pod-parsing framework

L<Pod::Simple::Methody> -- like Pod::Simple, but each sort of event
calls its own method (like C<start_head3>)

L<Pod::Simple::PullParser> -- a Pod-parsing framework like Pod::Simple,
but with a token-stream interface

L<Pod::Simple::SimpleTree> -- a Pod-parsing framework like Pod::Simple,
but with a tree interface

L<Pod::Simple::Checker> -- a simple Pod::Simple subclass that reads
documents, and then makes a plaintext report of any errors found in the
document

L<Pod::Simple::DumpAsXML> -- for dumping Pod documents as tidily
indented XML, showing each event on its own line

L<Pod::Simple::XMLOutStream> -- dumps a Pod document as XML (without
introducing extra whitespace as Pod::Simple::DumpAsXML does).

L<Pod::Simple::DumpAsText> -- for dumping Pod documents as tidily
indented text, showing each event on its own line

L<Pod::Simple::LinkSection> -- class for objects representing the values
of the TODO and TODO attributes of LE<lt>...E<gt> elements

L<Pod::Escapes> -- the module the Pod::Simple uses for evaluating
EE<lt>...E<gt> content

L<Pod::Simple::Text> -- a simple plaintext formatter for Pod

L<Pod::Simple::TextContent> -- like Pod::Simple::Text, but
makes no effort for indent or wrap the text being formatted

L<perlpod|perlpod>

L<perlpodspec|perlpodspec>

L<perldoc>


=head1 COPYRIGHT AND DISCLAIMERS

Copyright (c) 2002 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 C<[e-mail]>


=for notes
Hm, my old podchecker version (1.2) says:
 *** WARNING: node 'http://search.cpan.org/' contains non-escaped | or / at line 38 in file Subclassing.pod
 *** WARNING: node 'http://lists.perl.org/showlist.cgi?name=pod-people' contains non-escaped | or / at line 41 in file Subclassing.pod
Yes, L<...> is hard.


=cut