


Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


NAME
       Pod::Parser - base class for creating POD filters and
       translators

SYNOPSIS
           use Pod::Parser;

           package MyParser;
           @ISA = qw(Pod::Parser);

           sub command {
               my ($parser, $command, $paragraph, $line_num) = @_;
               ## Interpret the command and its text; sample actions might be:
               if ($command eq 'head1') { ... }
               elsif ($command eq 'head2') { ... }
               ## ... other commands and their actions
               my $out_fh = $parser->output_handle();
               my $expansion = $parser->interpolate($paragraph, $line_num);
               print $out_fh $expansion;
           }

           sub verbatim {
               my ($parser, $paragraph, $line_num) = @_;
               ## Format verbatim paragraph; sample actions might be:
               my $out_fh = $parser->output_handle();
               print $out_fh $paragraph;
           }

           sub textblock {
               my ($parser, $paragraph, $line_num) = @_;
               ## Translate/Format this block of text; sample actions might be:
               my $out_fh = $parser->output_handle();
               my $expansion = $parser->interpolate($paragraph, $line_num);
               print $out_fh $expansion;
           }

           sub interior_sequence {
               my ($parser, $seq_command, $seq_argument) = @_;
               ## Expand an interior sequence; sample actions might be:
               return "*$seq_argument*"     if ($seq_command eq 'B');
               return "`$seq_argument'"     if ($seq_command eq 'C');
               return "_${seq_argument}_'"  if ($seq_command eq 'I');
               ## ... other sequence commands and their resulting text
           }

           package main;

           ## Create a parser object and have it parse file whose name was
           ## given on the command-line (use STDIN if no files were given).
           $parser = new MyParser();
           $parser->parse_from_filehandle(\*STDIN)  if (@ARGV == 0);
           for (@ARGV) { $parser->parse_from_file($_); }





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Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


REQUIRES
       perl5.005, Pod::InputObjects, Exporter, Symbol, Carp

EXPORTS
       Nothing.

DESCRIPTION
       Pod::Parser is a base class for creating POD filters and
       translators.  It handles most of the effort involved with
       parsing the POD sections from an input stream, leaving
       subclasses free to be concerned only with performing the
       actual translation of text.

       Pod::Parser parses PODs, and makes method calls to handle
       the various components of the POD. Subclasses of
       Pod::Parser override these methods to translate the POD
       into whatever output format they desire.

QUICK OVERVIEW
       To create a POD filter for translating POD documentation
       into some other format, you create a subclass of
       Pod::Parser which typically overrides just the base class
       implementation for the following methods:

       o command()

       o verbatim()

       o textblock()

       o interior_sequence()

       You may also want to override the begin_input() and
       end_input() methods for your subclass (to perform any
       needed per-file and/or per-document initialization or
       cleanup).

       If you need to perform any preprocesssing of input before
       it is parsed you may want to override one or more of pre-
       process_line() and/or preprocess_paragraph().

       Sometimes it may be necessary to make more than one pass
       over the input files. If this is the case you have several
       options. You can make the first pass using Pod::Parser and
       override your methods to store the intermediate results in
       memory somewhere for the end_pod() method to process. You
       could use Pod::Parser for several passes with an appropri-
       ate state variable to control the operation for each pass.
       If your input source can't be reset to start at the begin-
       ning, you can store it in some other structure as a string
       or an array and have that structure implement a getline()
       method (which is all that parse_from_filehandle() uses to
       read input).




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       Feel free to add any member data fields you need to keep
       track of things like current font, indentation, horizontal
       or vertical position, or whatever else you like. Be sure
       to read the section on "PRIVATE METHODS AND DATA" to avoid
       name collisions.

       For the most part, the Pod::Parser base class should be
       able to do most of the input parsing for you and leave you
       free to worry about how to intepret the commands and
       translate the result.

       Note that all we have described here in this quick
       overview is the simplest most straightforward use of
       Pod::Parser to do stream-based parsing. It is also possi-
       ble to use the Pod::Parser::parse_text function to do more
       sophisticated tree-based parsing. See the section on
       "TREE-BASED PARSING".

PARSING OPTIONS
       A parse-option is simply a named option of Pod::Parser
       with a value that corresponds to a certain specified
       behavior. These various behaviors of Pod::Parser may be
       enabled/disabled by setting or or unsetting one or more
       parse-options using the parseopts() method.  The set of
       currently accepted parse-options is as follows:

       -want_nonPODs (default: unset)
          Normally (by default) Pod::Parser will only provide
          access to the POD sections of the input. Input para-
          graphs that are not part of the POD-format documenta-
          tion are not made available to the caller (not even
          using preprocess_paragraph()). Setting this option to a
          non-empty, non-zero value will allow preprocess_para-
          graph() to see non-POD sections of the input as well as
          POD sections. The cutting() method can be used to
          determine if the corresponding paragraph is a POD para-
          graph, or some other input paragraph.

       -process_cut_cmd (default: unset)
          Normally (by default) Pod::Parser handles the "=cut"
          POD directive by itself and does not pass it on to the
          caller for processing. Setting this option to a non-
          empty, non-zero value will cause Pod::Parser to pass
          the "=cut" directive to the caller just like any other
          POD command (and hence it may be processed by the com-
          mand() method).

          Pod::Parser will still interpret the "=cut" directive
          to mean that "cutting mode" has been (re)entered, but
          the caller will get a chance to capture the actual
          "=cut" paragraph itself for whatever purpose it
          desires.





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       -warnings (default: unset)
          Normally (by default) Pod::Parser recognizes a bare
          minimum of pod syntax errors and warnings and issues
          diagnostic messages for errors, but not for warnings.
          (Use Pod::Checker to do more thorough checking of POD
          syntax.) Setting this option to a non-empty, non-zero
          value will cause Pod::Parser to issue diagnostics for
          the few warnings it recognizes as well as the errors.

       Please see the section on "parseopts()" for a complete
       description of the interface for the setting and unsetting
       of parse-options.

RECOMMENDED SUBROUTINE/METHOD OVERRIDES
       Pod::Parser provides several methods which most subclasses
       will probably want to override. These methods are as fol-
       lows:

command()
                   $parser->command($cmd,$text,$line_num,$pod_para);

       This method should be overridden by subclasses to take the
       appropriate action when a POD command paragraph (denoted
       by a line beginning with "=") is encountered. When such a
       POD directive is seen in the input, this method is called
       and is passed:

       ""$cmd""
          the name of the command for this POD paragraph

       ""$text""
          the paragraph text for the given POD paragraph command.

       ""$line_num""
          the line-number of the beginning of the paragraph

       ""$pod_para""
          a reference to a "Pod::Paragraph" object which contains
          further information about the paragraph command (see
          the Pod::InputObjects manpage for details).

       Note that this method is called for "=pod" paragraphs.

       The base class implementation of this method simply treats
       the raw POD command as normal block of paragraph text
       (invoking the textblock() method with the command para-
       graph).

verbatim()
                   $parser->verbatim($text,$line_num,$pod_para);

       This method may be overridden by subclasses to take the
       appropriate action when a block of verbatim text is
       encountered. It is passed the following parameters:



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       ""$text""
          the block of text for the verbatim paragraph

       ""$line_num""
          the line-number of the beginning of the paragraph

       ""$pod_para""
          a reference to a "Pod::Paragraph" object which contains
          further information about the paragraph (see the
          Pod::InputObjects manpage for details).

       The base class implementation of this method simply prints
       the textblock (unmodified) to the output filehandle.

textblock()
                   $parser->textblock($text,$line_num,$pod_para);

       This method may be overridden by subclasses to take the
       appropriate action when a normal block of POD text is
       encountered (although the base class method will usually
       do what you want). It is passed the following parameters:

       ""$text""
          the block of text for the a POD paragraph

       ""$line_num""
          the line-number of the beginning of the paragraph

       ""$pod_para""
          a reference to a "Pod::Paragraph" object which contains
          further information about the paragraph (see the
          Pod::InputObjects manpage for details).

       In order to process interior sequences, subclasses imple-
       mentations of this method will probably want to invoke
       either interpolate() or parse_text(), passing it the text
       block "$text", and the corresponding line number in
       "$line_num", and then perform any desired processing upon
       the returned result.

       The base class implementation of this method simply prints
       the text block as it occurred in the input stream).

interior_sequence()
                   $parser->interior_sequence($seq_cmd,$seq_arg,$pod_seq);

       This method should be overridden by subclasses to take the
       appropriate action when an interior sequence is encoun-
       tered. An interior sequence is an embedded command within
       a block of text which appears as a command name (usually a
       single uppercase character) followed immediately by a
       string of text which is enclosed in angle brackets. This
       method is passed the sequence command "$seq_cmd" and the
       corresponding text "$seq_arg". It is invoked by the



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       interpolate() method for each interior sequence that
       occurs in the string that it is passed. It should return
       the desired text string to be used in place of the inte-
       rior sequence.  The "$pod_seq" argument is a reference to
       a "Pod::InteriorSequence" object which contains further
       information about the interior sequence.  Please see the
       Pod::InputObjects manpage for details if you need to
       access this additional information.

       Subclass implementations of this method may wish to invoke
       the nested() method of "$pod_seq" to see if it is nested
       inside some other interior-sequence (and if so, which
       kind).

       The base class implementation of the interior_sequence()
       method simply returns the raw text of the interior
       sequence (as it occurred in the input) to the caller.

OPTIONAL SUBROUTINE/METHOD OVERRIDES
       Pod::Parser provides several methods which subclasses may
       want to override to perform any special pre/post-process-
       ing. These methods do not have to be overridden, but it
       may be useful for subclasses to take advantage of them.

new()
                   my $parser = Pod::Parser->new();

       This is the constructor for Pod::Parser and its sub-
       classes. You do not need to override this method! It is
       capable of constructing subclass objects as well as base
       class objects, provided you use any of the following con-
       structor invocation styles:

           my $parser1 = MyParser->new();
           my $parser2 = new MyParser();
           my $parser3 = $parser2->new();

       where "MyParser" is some subclass of Pod::Parser.

       Using the syntax "MyParser::new()" to invoke the construc-
       tor is not recommended, but if you insist on being able to
       do this, then the subclass will need to override the new()
       constructor method. If you do override the constructor,
       you must be sure to invoke the initialize() method of the
       newly blessed object.

       Using any of the above invocations, the first argument to
       the constructor is always the corresponding package name
       (or object reference). No other arguments are required,
       but if desired, an associative array (or hash-table) my be
       passed to the new() constructor, as in:

           my $parser1 = MyParser->new( MYDATA => $value1, MOREDATA => $value2 );
           my $parser2 = new MyParser( -myflag => 1 );



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       All arguments passed to the new() constructor will be
       treated as key/value pairs in a hash-table. The newly con-
       structed object will be initialized by copying the con-
       tents of the given hash-table (which may have been empty).
       The new() constructor for this class and all of its sub-
       classes returns a blessed reference to the initialized
       object (hash-table).

initialize()
                   $parser->initialize();

       This method performs any necessary object initialization.
       It takes no arguments (other than the object instance of
       course, which is typically copied to a local variable
       named "$self"). If subclasses override this method then
       they must be sure to invoke "$self->SUPER::initialize()".

begin_pod()
                   $parser->begin_pod();

       This method is invoked at the beginning of processing for
       each POD document that is encountered in the input. Sub-
       classes should override this method to perform any per-
       document initialization.

begin_input()
                   $parser->begin_input();

       This method is invoked by parse_from_filehandle() immedi-
       ately before processing input from a filehandle. The base
       class implementation does nothing, however, subclasses may
       override it to perform any per-file initializations.

       Note that if multiple files are parsed for a single POD
       document (perhaps the result of some future "=include"
       directive) this method is invoked for every file that is
       parsed. If you wish to perform certain initializations
       once per document, then you should use begin_pod().

end_input()
                   $parser->end_input();

       This method is invoked by parse_from_filehandle() immedi-
       ately after processing input from a filehandle. The base
       class implementation does nothing, however, subclasses may
       override it to perform any per-file cleanup actions.

       Please note that if multiple files are parsed for a single
       POD document (perhaps the result of some kind of
       "=include" directive) this method is invoked for every
       file that is parsed. If you wish to perform certain
       cleanup actions once per document, then you should use
       end_pod().




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end_pod()
                   $parser->end_pod();

       This method is invoked at the end of processing for each
       POD document that is encountered in the input. Subclasses
       should override this method to perform any per-document
       finalization.

preprocess_line()
                 $textline = $parser->preprocess_line($text, $line_num);

       This method should be overridden by subclasses that wish
       to perform any kind of preprocessing for each line of
       input (before it has been determined whether or not it is
       part of a POD paragraph). The parameter "$text" is the
       input line; and the parameter "$line_num" is the line num-
       ber of the corresponding text line.

       The value returned should correspond to the new text to
       use in its place.  If the empty string or an undefined
       value is returned then no further processing will be per-
       formed for this line.

       Please note that the preprocess_line() method is invoked
       before the preprocess_paragraph() method. After all (pos-
       sibly preprocessed) lines in a paragraph have been assem-
       bled together and it has been determined that the para-
       graph is part of the POD documentation from one of the
       selected sections, then preprocess_paragraph() is invoked.

       The base class implementation of this method returns the
       given text.

preprocess_paragraph()
                   $textblock = $parser->preprocess_paragraph($text, $line_num);

       This method should be overridden by subclasses that wish
       to perform any kind of preprocessing for each block (para-
       graph) of POD documentation that appears in the input
       stream. The parameter "$text" is the POD paragraph from
       the input file; and the parameter "$line_num" is the line
       number for the beginning of the corresponding paragraph.

       The value returned should correspond to the new text to
       use in its place If the empty string is returned or an
       undefined value is returned, then the given "$text" is
       ignored (not processed).

       This method is invoked after gathering up all the lines in
       a paragraph and after determining the cutting state of the
       paragraph, but before trying to further parse or interpret
       them. After preprocess_paragraph() returns, the current
       cutting state (which is returned by "$self->cutting()") is
       examined. If it evaluates to true then input text



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       (including the given "$text") is cut (not processed) until
       the next POD directive is encountered.

       Please note that the preprocess_line() method is invoked
       before the preprocess_paragraph() method. After all (pos-
       sibly preprocessed) lines in a paragraph have been assem-
       bled together and either it has been determined that the
       paragraph is part of the POD documentation from one of the
       selected sections or the "-want_nonPODs" option is true,
       then preprocess_paragraph() is invoked.

       The base class implementation of this method returns the
       given text.

METHODS FOR PARSING AND PROCESSING
       Pod::Parser provides several methods to process input
       text. These methods typically won't need to be overridden
       (and in some cases they can't be overridden), but sub-
       classes may want to invoke them to exploit their function-
       ality.

parse_text()
                   $ptree1 = $parser->parse_text($text, $line_num);
                   $ptree2 = $parser->parse_text({%opts}, $text, $line_num);
                   $ptree3 = $parser->parse_text(\%opts, $text, $line_num);

       This method is useful if you need to perform your own
       interpolation of interior sequences and can't rely upon
       interpolate to expand them in simple bottom-up order
       order.

       The parameter "$text" is a string or block of text to be
       parsed for interior sequences; and the parameter
       "$line_num" is the line number curresponding to the begin-
       ning of "$text".

       parse_text() will parse the given text into a parse-tree
       of "nodes."  and interior-sequences.  Each "node" in the
       parse tree is either a text-string, or a Pod::InteriorSe-
       quence.  The result returned is a parse-tree of type
       Pod::ParseTree. Please see the Pod::InputObjects manpage
       for more information about Pod::InteriorSequence and
       Pod::ParseTree.

       If desired, an optional hash-ref may be specified as the
       first argument to customize certain aspects of the parse-
       tree that is created and returned. The set of recognized
       option keywords are:

       -expand_seq => code-ref|method-name
          Normally, the parse-tree returned by parse_text() will
          contain an unexpanded "Pod::InteriorSequence" object
          for each interior-sequence encountered. Specifying
          -expand_seq tells parse_text() to "expand" every



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          interior-sequence it sees by invoking the referenced
          function (or named method of the parser object) and
          using the return value as the expanded result.

          If a subroutine reference was given, it is invoked as:

            &$code_ref( $parser, $sequence )

          and if a method-name was given, it is invoked as:

            $parser->method_name( $sequence )

          where "$parser" is a reference to the parser object,
          and "$sequence" is a reference to the interior-sequence
          object.  [NOTE: If the interior_sequence() method is
          specified, then it is invoked according to the inter-
          face specified in the section on "inte-
          rior_sequence()"].

       -expand_text => code-ref|method-name
          Normally, the parse-tree returned by parse_text() will
          contain a text-string for each contiguous sequence of
          characters outside of an interior-sequence. Specifying
          -expand_text tells parse_text() to "preprocess" every
          such text-string it sees by invoking the referenced
          function (or named method of the parser object) and
          using the return value as the preprocessed (or
          "expanded") result. [Note that if the result is an
          interior-sequence, then it will not be expanded as
          specified by the -expand_seq option; Any such recursive
          expansion needs to be handled by the specified callback
          routine.]

          If a subroutine reference was given, it is invoked as:

            &$code_ref( $parser, $text, $ptree_node )

          and if a method-name was given, it is invoked as:

            $parser->method_name( $text, $ptree_node )

          where "$parser" is a reference to the parser object,
          "$text" is the text-string encountered, and
          "$ptree_node" is a reference to the current node in the
          parse-tree (usually an interior-sequence object or else
          the top-level node of the parse-tree).

       -expand_ptree => code-ref|method-name
          Rather than returning a "Pod::ParseTree", pass the
          parse-tree as an argument to the referenced subroutine
          (or named method of the parser object) and return the
          result instead of the parse-tree object.

          If a subroutine reference was given, it is invoked as:



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            &$code_ref( $parser, $ptree )

          and if a method-name was given, it is invoked as:

            $parser->method_name( $ptree )

          where "$parser" is a reference to the parser object,
          and "$ptree" is a reference to the parse-tree object.

interpolate()
                   $textblock = $parser->interpolate($text, $line_num);

       This method translates all text (including any embedded
       interior sequences) in the given text string "$text" and
       returns the interpolated result. The parameter "$line_num"
       is the line number corresponding to the beginning of
       "$text".

       interpolate() merely invokes a private method to recur-
       sively expand nested interior sequences in bottom-up order
       (innermost sequences are expanded first). If there is a
       need to expand nested sequences in some alternate order,
       use parse_text instead.

parse_from_filehandle()
                   $parser->parse_from_filehandle($in_fh,$out_fh);

       This method takes an input filehandle (which is assumed to
       already be opened for reading) and reads the entire input
       stream looking for blocks (paragraphs) of POD documenta-
       tion to be processed. If no first argument is given the
       default input filehandle "STDIN" is used.

       The "$in_fh" parameter may be any object that provides a
       getline() method to retrieve a single line of input text
       (hence, an appropriate wrapper object could be used to
       parse PODs from a single string or an array of strings).

       Using "$in_fh->getline()", input is read line-by-line and
       assembled into paragraphs or "blocks" (which are separated
       by lines containing nothing but whitespace). For each
       block of POD documentation encountered it will invoke a
       method to parse the given paragraph.

       If a second argument is given then it should correspond to
       a filehandle where output should be sent (otherwise the
       default output filehandle is "STDOUT" if no output file-
       handle is currently in use).

       NOTE: For performance reasons, this method caches the
       input stream at the top of the stack in a local variable.
       Any attempts by clients to change the stack contents dur-
       ing processing when in the midst executing of this method
       will not affect the input stream used by the current



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       invocation of this method.

       This method does not usually need to be overridden by sub-
       classes.

parse_from_file()
                   $parser->parse_from_file($filename,$outfile);

       This method takes a filename and does the following:

       o opens the input and output files for reading (creating
         the appropriate filehandles)

       o invokes the parse_from_filehandle() method passing it
         the corresponding input and output filehandles.

       o closes the input and output files.

       If the special input filename "-" or "<&STDIN" is given
       then the STDIN filehandle is used for input (and no open
       or close is performed). If no input filename is specified
       then "-" is implied.

       If a second argument is given then it should be the name
       of the desired output file. If the special output filename
       "-" or ">&STDOUT" is given then the STDOUT filehandle is
       used for output (and no open or close is performed). If
       the special output filename ">&STDERR" is given then the
       STDERR filehandle is used for output (and no open or close
       is performed). If no output filehandle is currently in use
       and no output filename is specified, then "-" is implied.

       This method does not usually need to be overridden by sub-
       classes.

ACCESSOR METHODS
       Clients of Pod::Parser should use the following methods to
       access instance data fields:

errorsub()
                   $parser->errorsub("method_name");
                   $parser->errorsub(\&warn_user);
                   $parser->errorsub(sub { print STDERR, @_ });

       Specifies the method or subroutine to use when printing
       error messages about POD syntax. The supplied method/sub-
       routine must return TRUE upon successful printing of the
       message. If "undef" is given, then the warn builtin is
       used to issue error messages (this is the default behav-
       ior).







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                   my $errorsub = $parser->errorsub()
                   my $errmsg = "This is an error message!\n"
                   (ref $errorsub) and &{$errorsub}($errmsg)
                       or (defined $errorsub) and $parser->$errorsub($errmsg)
                           or  warn($errmsg);

       Returns a method name, or else a reference to the user-
       supplied subroutine used to print error messages. Returns
       "undef" if the warn builtin is used to issue error mes-
       sages (this is the default behavior).

cutting()
                   $boolean = $parser->cutting();

       Returns the current "cutting" state: a boolean-valued
       scalar which evaluates to true if text from the input file
       is currently being "cut" (meaning it is not considered
       part of the POD document).

                   $parser->cutting($boolean);

       Sets the current "cutting" state to the given value and
       returns the result.

parseopts()
       When invoked with no additional arguments, parseopts
       returns a hashtable of all the current parsing options.

                   ## See if we are parsing non-POD sections as well as POD ones
                   my %opts = $parser->parseopts();
                   $opts{'-want_nonPODs}' and print "-want_nonPODs\n";

       When invoked using a single string, parseopts treats the
       string as the name of a parse-option and returns its cor-
       responding value if it exists (returns "undef" if it
       doesn't).

                   ## Did we ask to see '=cut' paragraphs?
                   my $want_cut = $parser->parseopts('-process_cut_cmd');
                   $want_cut and print "-process_cut_cmd\n";

       When invoked with multiple arguments, parseopts treats
       them as key/value pairs and the specified parse-option
       names are set to the given values. Any unspecified parse-
       options are unaffected.

                   ## Set them back to the default
                   $parser->parseopts(-warnings => 0);

       When passed a single hash-ref, parseopts uses that hash to
       completely reset the existing parse-options, all previous
       parse-option values are lost.





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                   ## Reset all options to default
                   $parser->parseopts( { } );

       See the section on "PARSING OPTIONS" for more information
       on the name and meaning of each parse-option currently
       recognized.

output_file()
                   $fname = $parser->output_file();

       Returns the name of the output file being written.

output_handle()
                   $fhandle = $parser->output_handle();

       Returns the output filehandle object.

input_file()
                   $fname = $parser->input_file();

       Returns the name of the input file being read.

input_handle()
                   $fhandle = $parser->input_handle();

       Returns the current input filehandle object.

PRIVATE METHODS AND DATA
       Pod::Parser makes use of several internal methods and data
       fields which clients should not need to see or use. For
       the sake of avoiding name collisions for client data and
       methods, these methods and fields are briefly discussed
       here. Determined hackers may obtain further information
       about them by reading the Pod::Parser source code.

       Private data fields are stored in the hash-object whose
       reference is returned by the new() constructor for this
       class. The names of all private methods and data-fields
       used by Pod::Parser begin with a prefix of "_" and match
       the regular expression "/^_\w+$/".

TREE-BASED PARSING
       If straightforward stream-based parsing wont meet your
       needs (as is likely the case for tasks such as translating
       PODs into structured markup languages like HTML and XML)
       then you may need to take the tree-based approach. Rather
       than doing everything in one pass and calling the interpo-
       late() method to expand sequences into text, it may be
       desirable to instead create a parse-tree using the
       parse_text() method to return a tree-like structure which
       may contain an ordered list list of children (each of
       which may be a text-string, or a similar tree-like struc-
       ture).




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Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


       Pay special attention to the section on "METHODS FOR PARS-
       ING AND PROCESSING" and to the objects described in the
       Pod::InputObjects manpage. The former describes the gory
       details and parameters for how to customize and extend the
       parsing behavior of Pod::Parser. Pod::InputObjects pro-
       vides several objects that may all be used interchangeably
       as parse-trees. The most obvious one is the Pod::ParseTree
       object. It defines the basic interface and functionality
       that all things trying to be a POD parse-tree should do. A
       Pod::ParseTree is defined such that each "node" may be a
       text-string, or a reference to another parse-tree.  Each
       Pod::Paragraph object and each Pod::InteriorSequence
       object also supports the basic parse-tree interface.

       The parse_text() method takes a given paragraph of text,
       and returns a parse-tree that contains one or more chil-
       dren, each of which may be a text-string, or an Interi-
       orSequence object. There are also callback-options that
       may be passed to parse_text() to customize the way it
       expands or transforms interior-sequences, as well as the
       returned result. These callbacks can be used to create a
       parse-tree with custom-made objects (which may or may not
       support the parse-tree interface, depending on how you
       choose to do it).

       If you wish to turn an entire POD document into a parse-
       tree, that process is fairly straightforward. The
       parse_text() method is the key to doing this successfully.
       Every paragraph-callback (i.e. the polymorphic methods for
       command(), verbatim(), and textblock() paragraphs) takes a
       Pod::Paragraph object as an argument. Each paragraph
       object has a parse_tree() method that can be used to get
       or set a corresponding parse-tree. So for each of those
       paragraph-callback methods, simply call parse_text() with
       the options you desire, and then use the returned parse-
       tree to assign to the given paragraph object.

       That gives you a parse-tree for each paragraph - so now
       all you need is an ordered list of paragraphs. You can
       maintain that yourself as a data element in the
       object/hash. The most straightforward way would be simply
       to use an array-ref, with the desired set of custom
       "options" for each invocation of parse_text. Let's assume
       the desired option-set is given by the hash "%options".
       Then we might do something like the following:

           package MyPodParserTree;

           @ISA = qw( Pod::Parser );

           ...






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Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


           sub begin_pod {
               my $self = shift;
               $self->{'-paragraphs'} = [];  ## initialize paragraph list
           }

           sub command {
               my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
               my $ptree = $parser->parse_text({%options}, $paragraph, ...);
               $pod_para->parse_tree( $ptree );
               push @{ $self->{'-paragraphs'} }, $pod_para;
           }

           sub verbatim {
               my ($parser, $paragraph, $line_num, $pod_para) = @_;
               push @{ $self->{'-paragraphs'} }, $pod_para;
           }

           sub textblock {
               my ($parser, $paragraph, $line_num, $pod_para) = @_;
               my $ptree = $parser->parse_text({%options}, $paragraph, ...);
               $pod_para->parse_tree( $ptree );
               push @{ $self->{'-paragraphs'} }, $pod_para;
           }

           ...

           package main;
           ...
           my $parser = new MyPodParserTree(...);
           $parser->parse_from_file(...);
           my $paragraphs_ref = $parser->{'-paragraphs'};

       Of course, in this module-author's humble opinion, I'd be
       more inclined to use the existing Pod::ParseTree object
       than a simple array. That way everything in it, paragraphs
       and sequences, all respond to the same core interface for
       all parse-tree nodes. The result would look something
       like:

           package MyPodParserTree2;

           ...

           sub begin_pod {
               my $self = shift;
               $self->{'-ptree'} = new Pod::ParseTree;  ## initialize parse-tree
           }

           sub parse_tree {
               ## convenience method to get/set the parse-tree for the entire POD
               (@_ > 1)  and  $_[0]->{'-ptree'} = $_[1];
               return $_[0]->{'-ptree'};
           }




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Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


           sub command {
               my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
               my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
               $pod_para->parse_tree( $ptree );
               $parser->parse_tree()->append( $pod_para );
           }

           sub verbatim {
               my ($parser, $paragraph, $line_num, $pod_para) = @_;
               $parser->parse_tree()->append( $pod_para );
           }

           sub textblock {
               my ($parser, $paragraph, $line_num, $pod_para) = @_;
               my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
               $pod_para->parse_tree( $ptree );
               $parser->parse_tree()->append( $pod_para );
           }

           ...

           package main;
           ...
           my $parser = new MyPodParserTree2(...);
           $parser->parse_from_file(...);
           my $ptree = $parser->parse_tree;
           ...

       Now you have the entire POD document as one great big
       parse-tree. You can even use the -expand_seq option to
       parse_text to insert whole different kinds of objects.
       Just don't expect Pod::Parser to know what to do with them
       after that. That will need to be in your code. Or, alter-
       natively, you can insert any object you like so long as it
       conforms to the Pod::ParseTree interface.

       One could use this to create subclasses of Pod::Paragraphs
       and Pod::InteriorSequences for specific commands (or to
       create your own custom node-types in the parse-tree) and
       add some kind of emit() method to each custom node/sub-
       class object in the tree. Then all you'd need to do is
       recursively walk the tree in the desired order, processing
       the children (most likely from left to right) by format-
       ting them if they are text-strings, or by calling their
       emit() method if they are objects/references.

SEE ALSO
       the Pod::InputObjects manpage, the Pod::Select manpage

       Pod::InputObjects defines POD input objects corresponding
       to command paragraphs, parse-trees, and interior-
       sequences.

       Pod::Select is a subclass of Pod::Parser which provides



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Pod::Parser(3p)  Perl Programmers Reference Guide Pod::Parser(3p)


       the ability to selectively include and/or exclude sections
       of a POD document from being translated based upon the
       current heading, subheading, subsubheading, etc.

AUTHOR
       Brad Appleton <bradapp@enteract.com>

       Based on code for Pod::Text written by Tom Christiansen
       <tchrist@mox.perl.com>
















































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