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




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) { $parser->parse_from_file($_); }


REQUIRES

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


EXPORTS

       Nothing.


DESCRIPTION

       NOTE: This module is considered legacy; modern Perl releases (5.18 and
       higher) are going to remove Pod-Parser from core and use Pod-Simple for
       all things POD.

       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 preprocessing of input before it is parsed
       you may want to override one or more of preprocess_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
       appropriate state variable to control the operation for each pass. If
       your input source can't be reset to start at the beginning, 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).

       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 "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
       interpret 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 possible to use the Pod::Parser::parse_text
       function to do more sophisticated tree-based parsing. See "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
       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 paragraphs that are not part of the
          POD-format documentation 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_paragraph() 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 paragraph, 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 command()
          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.

       -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 "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 follows:


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 Pod::InputObjects 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 paragraph).


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:

       $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 Pod::InputObjects 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 Pod::InputObjects for details).

       In order to process interior sequences, subclasses implementations 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 encountered. 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 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
       interior sequence.  The $pod_seq argument is a reference to a
       "Pod::InteriorSequence" object which contains further information about
       the interior sequence.  Please see Pod::InputObjects 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-processing. 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 subclasses. 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 constructor 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 constructor 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 );

       All arguments passed to the new() constructor will be treated as
       key/value pairs in a hash-table. The newly constructed object will be
       initialized by copying the contents of the given hash-table (which may
       have been empty). The new() constructor for this class and all of its
       subclasses 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. Subclasses should override
       this method to perform any per-document initialization.


begin_input()

                   $parser->begin_input();

       This method is invoked by parse_from_filehandle() immediately 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() immediately 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().


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 number
       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 performed for this line.

       Please note that the preprocess_line() method is invoked before the
       preprocess_paragraph() method. After all (possibly preprocessed) lines
       in a paragraph have been assembled together and it has been determined
       that the paragraph 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 (paragraph) 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 (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 (possibly preprocessed) lines
       in a paragraph have been assembled 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 subclasses may want to invoke them to exploit
       their functionality.


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.

       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
       corresponding to the beginning 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::InteriorSequence.  The result returned is a
       parse-tree of type Pod::ParseTree. Please see Pod::InputObjects 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 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 interface specified in "interior_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:

            &$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 recursively 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 documentation 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 filehandle 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 during processing when in the midst executing
       of this method will not affect the input stream used by the current
       invocation of this method.

       This method does not usually need to be overridden by subclasses.


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. Filehandle
       references, or objects that support the regular IO operations (like
       "<$fh>" or "$fh-<Egt"getline>) are also accepted; the handles must
       already be opened.

       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.  Alternatively, filehandle
       references or objects that support the regular IO operations (like
       "print", e.g. IO::String) are also accepted; the object must already be
       opened.

       This method does not usually need to be overridden by subclasses.


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/subroutine must return TRUE upon
       successful printing of the message. If "undef" is given, then the carp
       builtin is used to issue error messages (this is the default behavior).

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

       Returns a method name, or else a reference to the user-supplied
       subroutine used to print error messages. Returns "undef" if the carp
       builtin is used to issue error messages (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 corresponding 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.

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

       See "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 interpolate() 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 of
       children (each of which may be a text-string, or a similar tree-like
       structure).

       Pay special attention to "METHODS FOR PARSING AND PROCESSING" and to
       the objects described in Pod::InputObjects. The former describes the
       gory details and parameters for how to customize and extend the parsing
       behavior of Pod::Parser. Pod::InputObjects provides 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 children, each of which may be a
       text-string, or an InteriorSequence 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 );

           ...

           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'};
           }

           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,
       alternatively, 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/subclass 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 formatting them if they
       are text-strings, or by calling their emit() method if they are
       objects/references.


CAVEATS

       Please note that POD has the notion of "paragraphs": this is something
       starting after a blank (read: empty) line, with the single exception of
       the file start, which is also starting a paragraph. That means that
       especially a command (e.g. "=head1") must be preceded with a blank
       line; "__END__" is not a blank line.


SEE ALSO

       Pod::InputObjects(3), Pod::Select(3)

       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 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

       Please report bugs using <http://rt.cpan.org>.

       Brad Appleton <bradapp@enteract.com>

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


LICENSE

       Pod-Parser is free software; you can redistribute it and/or modify it
       under the terms of the Artistic License distributed with Perl version
       5.000 or (at your option) any later version. Please refer to the
       Artistic License that came with your Perl distribution for more
       details. If your version of Perl was not distributed under the terms of
       the Artistic License, than you may distribute PodParser under the same
       terms as Perl itself.



perl v5.24.0                      2016-03-01                  Pod::Parser(3pm)

perl 5.24 - Generated Sat Nov 19 10:02:26 CST 2016
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