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#############################################################################

# Pod/Checker.pm -- check pod documents for syntax errors

#

# Copyright (C) 1994-2000 by Bradford Appleton. All rights reserved.

# This file is part of "PodParser". PodParser is free software;

# you can redistribute it and/or modify it under the same terms

# as Perl itself.

#############################################################################

package Pod::Checker;

use strict;

use vars qw($VERSION @ISA @EXPORT %VALID_COMMANDS %VALID_SEQUENCES);

$VERSION = '1.45';  ## Current version of this package

require  5.005;    ## requires this Perl version or later

use Pod::ParseUtils; ## for hyperlinks and lists

=head1 NAME

Pod::Checker, podchecker() - check pod documents for syntax errors

=head1 SYNOPSIS

  use Pod::Checker;

  $syntax_okay = podchecker($filepath, $outputpath, %options);

  my $checker = new Pod::Checker %options;

  $checker->parse_from_file($filepath, \*STDERR);

=head1 OPTIONS/ARGUMENTS

C<$filepath> is the input POD to read and C<$outputpath> is

where to write POD syntax error messages. Either argument may be a scalar

indicating a file-path, or else a reference to an open filehandle.

If unspecified, the input-file it defaults to C<\*STDIN>, and

the output-file defaults to C<\*STDERR>.

=head2 podchecker()

This function can take a hash of options:

=over 4

=item B<-warnings> =E<gt> I<val>

Turn warnings on/off. I<val> is usually 1 for on, but higher values

trigger additional warnings. See L<"Warnings">.

=back

=head1 DESCRIPTION

B<podchecker> will perform syntax checking of Perl5 POD format documentation.

Curious/ambitious users are welcome to propose additional features they wish

to see in B<Pod::Checker> and B<podchecker> and verify that the checks are

consistent with L<perlpod>.

The following checks are currently performed:

=over 4

=item *

Unknown '=xxxx' commands, unknown 'XE<lt>...E<gt>' interior-sequences,

and unterminated interior sequences.

=item *

Check for proper balancing of C<=begin> and C<=end>. The contents of such

a block are generally ignored, i.e. no syntax checks are performed.

=item *

Check for proper nesting and balancing of C<=over>, C<=item> and C<=back>.

=item *

Check for same nested interior-sequences (e.g.

C<LE<lt>...LE<lt>...E<gt>...E<gt>>).

=item *

Check for malformed or non-existing entities C<EE<lt>...E<gt>>.

=item *

Check for correct syntax of hyperlinks C<LE<lt>...E<gt>>. See L<perlpod>

for details.

=item *

Check for unresolved document-internal links. This check may also reveal

misspelled links that seem to be internal links but should be links

to something else.

=back

=head1 DIAGNOSTICS

=head2 Errors

=over 4

=item * empty =headn

A heading (C<=head1> or C<=head2>) without any text? That ain't no

heading!

=item * =over on line I<N> without closing =back

The C<=over> command does not have a corresponding C<=back> before the

next heading (C<=head1> or C<=head2>) or the end of the file.

=item * =item without previous =over

=item * =back without previous =over

An C<=item> or C<=back> command has been found outside a

C<=over>/C<=back> block.

=item * No argument for =begin

A C<=begin> command was found that is not followed by the formatter

specification.

=item * =end without =begin

A standalone C<=end> command was found.

=item * Nested =begin's

There were at least two consecutive C<=begin> commands without

the corresponding C<=end>. Only one C<=begin> may be active at

a time.

=item * =for without formatter specification

There is no specification of the formatter after the C<=for> command.

=item * unresolved internal link I<NAME>

The given link to I<NAME> does not have a matching node in the current

POD. This also happened when a single word node name is not enclosed in

C<"">.

=item * Unknown command "I<CMD>"

An invalid POD command has been found. Valid are C<=head1>, C<=head2>,

C<=head3>, C<=head4>, C<=over>, C<=item>, C<=back>, C<=begin>, C<=end>,

C<=for>, C<=pod>, C<=cut>

=item * Unknown interior-sequence "I<SEQ>"

An invalid markup command has been encountered. Valid are:

C<BE<lt>E<gt>>, C<CE<lt>E<gt>>, C<EE<lt>E<gt>>, C<FE<lt>E<gt>>,

C<IE<lt>E<gt>>, C<LE<lt>E<gt>>, C<SE<lt>E<gt>>, C<XE<lt>E<gt>>,

C<ZE<lt>E<gt>>

=item * nested commands I<CMD>E<lt>...I<CMD>E<lt>...E<gt>...E<gt>

Two nested identical markup commands have been found. Generally this

does not make sense.

=item * garbled entity I<STRING>

The I<STRING> found cannot be interpreted as a character entity.

=item * Entity number out of range

An entity specified by number (dec, hex, oct) is out of range (1-255).

=item * malformed link LE<lt>E<gt>

The link found cannot be parsed because it does not conform to the

syntax described in L<perlpod>.

=item * nonempty ZE<lt>E<gt>

The C<ZE<lt>E<gt>> sequence is supposed to be empty.

=item * empty XE<lt>E<gt>

The index entry specified contains nothing but whitespace.

=item * Spurious text after =pod / =cut

The commands C<=pod> and C<=cut> do not take any arguments.

=item * Spurious character(s) after =back

The C<=back> command does not take any arguments.

=back

=head2 Warnings

These may not necessarily cause trouble, but indicate mediocre style.

=over 4

=item * multiple occurrence of link target I<name>

The POD file has some C<=item> and/or C<=head> commands that have

the same text. Potential hyperlinks to such a text cannot be unique then.

This warning is printed only with warning level greater than one.

=item * line containing nothing but whitespace in paragraph

There is some whitespace on a seemingly empty line. POD is very sensitive

to such things, so this is flagged. B<vi> users switch on the B<list>

option to avoid this problem.

=begin _disabled_

=item * file does not start with =head

The file starts with a different POD directive than head.

This is most probably something you do not want.

=end _disabled_

=item * previous =item has no contents

There is a list C<=item> right above the flagged line that has no

text contents. You probably want to delete empty items.

=item * preceding non-item paragraph(s)

A list introduced by C<=over> starts with a text or verbatim paragraph,

but continues with C<=item>s. Move the non-item paragraph out of the

C<=over>/C<=back> block.

=item * =item type mismatch (I<one> vs. I<two>)

A list started with e.g. a bullet-like C<=item> and continued with a

numbered one. This is obviously inconsistent. For most translators the

type of the I<first> C<=item> determines the type of the list.

=item * I<N> unescaped C<E<lt>E<gt>> in paragraph

Angle brackets not written as C<E<lt>ltE<gt>> and C<E<lt>gtE<gt>>

can potentially cause errors as they could be misinterpreted as

markup commands. This is only printed when the -warnings level is

greater than 1.

=item * Unknown entity

A character entity was found that does not belong to the standard

ISO set or the POD specials C<verbar> and C<sol>.

=item * No items in =over

The list opened with C<=over> does not contain any items.

=item * No argument for =item

C<=item> without any parameters is deprecated. It should either be followed

by C<*> to indicate an unordered list, by a number (optionally followed

by a dot) to indicate an ordered (numbered) list or simple text for a

definition list.

=item * empty section in previous paragraph

The previous section (introduced by a C<=head> command) does not contain

any text. This usually indicates that something is missing. Note: A

C<=head1> followed immediately by C<=head2> does not trigger this warning.

=item * Verbatim paragraph in NAME section

The NAME section (C<=head1 NAME>) should consist of a single paragraph

with the script/module name, followed by a dash `-' and a very short

description of what the thing is good for.

=item * =headI<n> without preceding higher level

For example if there is a C<=head2> in the POD file prior to a

C<=head1>.

=back

=head2 Hyperlinks

There are some warnings with respect to malformed hyperlinks:

=over 4

=item * ignoring leading/trailing whitespace in link

There is whitespace at the beginning or the end of the contents of

LE<lt>...E<gt>.

=item * (section) in '$page' deprecated

There is a section detected in the page name of LE<lt>...E<gt>, e.g.

C<LE<lt>passwd(2)E<gt>>. POD hyperlinks may point to POD documents only.

Please write C<CE<lt>passwd(2)E<gt>> instead. Some formatters are able

to expand this to appropriate code. For links to (builtin) functions,

please say C<LE<lt>perlfunc/mkdirE<gt>>, without ().

=item * alternative text/node '%s' contains non-escaped | or /

The characters C<|> and C</> are special in the LE<lt>...E<gt> context.

Although the hyperlink parser does its best to determine which "/" is

text and which is a delimiter in case of doubt, one ought to escape

these literal characters like this:

  /     E<sol>

  |     E<verbar>

=back

=head1 RETURN VALUE

B<podchecker> returns the number of POD syntax errors found or -1 if

there were no POD commands at all found in the file.

=head1 EXAMPLES

See L</SYNOPSIS>

=head1 INTERFACE

While checking, this module collects document properties, e.g. the nodes

for hyperlinks (C<=headX>, C<=item>) and index entries (C<XE<lt>E<gt>>).

POD translators can use this feature to syntax-check and get the nodes in

a first pass before actually starting to convert. This is expensive in terms

of execution time, but allows for very robust conversions.

Since PodParser-1.24 the B<Pod::Checker> module uses only the B<poderror>

method to print errors and warnings. The summary output (e.g.

"Pod syntax OK") has been dropped from the module and has been included in

B<podchecker> (the script). This allows users of B<Pod::Checker> to

control completely the output behavior. Users of B<podchecker> (the script)

get the well-known behavior.

=cut

#############################################################################

#use diagnostics;

use Carp qw(croak);

use Exporter;

use Pod::Parser;

@ISA = qw(Pod::Parser);

@EXPORT = qw(&podchecker);

my %VALID_COMMANDS = (

    'pod'    =>  1,

    'cut'    =>  1,

    'head1'  =>  1,

    'head2'  =>  1,

    'head3'  =>  1,

    'head4'  =>  1,

    'over'   =>  1,

    'back'   =>  1,

    'item'   =>  1,

    'for'    =>  1,

    'begin'  =>  1,

    'end'    =>  1,

    'encoding' =>  1,

);

my %VALID_SEQUENCES = (

    'I'  =>  1,

    'B'  =>  1,

    'S'  =>  1,

    'C'  =>  1,

    'L'  =>  1,

    'F'  =>  1,

    'X'  =>  1,

    'Z'  =>  1,

    'E'  =>  1,

);

# stolen from HTML::Entities

my %ENTITIES = (

 # Some normal chars that have special meaning in SGML context

 amp    => '&',  # ampersand

'gt'    => '>',  # greater than

'lt'    => '<',  # less than

 quot   => '"',  # double quote

 # PUBLIC ISO 8879-1986//ENTITIES Added Latin 1//EN//HTML

 AElig  => 'Æ',  # capital AE diphthong (ligature)

 Aacute => 'Á',  # capital A, acute accent

 Acirc  => 'Â',  # capital A, circumflex accent

 Agrave => 'À',  # capital A, grave accent

 Aring  => 'Å',  # capital A, ring

 Atilde => 'Ã',  # capital A, tilde

 Auml   => 'Ä',  # capital A, dieresis or umlaut mark

 Ccedil => 'Ç',  # capital C, cedilla

 ETH    => 'Ð',  # capital Eth, Icelandic

 Eacute => 'É',  # capital E, acute accent

 Ecirc  => 'Ê',  # capital E, circumflex accent

 Egrave => 'È',  # capital E, grave accent

 Euml   => 'Ë',  # capital E, dieresis or umlaut mark

 Iacute => 'Í',  # capital I, acute accent

 Icirc  => 'Î',  # capital I, circumflex accent

 Igrave => 'Ì',  # capital I, grave accent

 Iuml   => 'Ï',  # capital I, dieresis or umlaut mark

 Ntilde => 'Ñ',  # capital N, tilde

 Oacute => 'Ó',  # capital O, acute accent

 Ocirc  => 'Ô',  # capital O, circumflex accent

 Ograve => 'Ò',  # capital O, grave accent

 Oslash => 'Ø',  # capital O, slash

 Otilde => 'Õ',  # capital O, tilde

 Ouml   => 'Ö',  # capital O, dieresis or umlaut mark

 THORN  => 'Þ',  # capital THORN, Icelandic

 Uacute => 'Ú',  # capital U, acute accent

 Ucirc  => 'Û',  # capital U, circumflex accent

 Ugrave => 'Ù',  # capital U, grave accent

 Uuml   => 'Ü',  # capital U, dieresis or umlaut mark

 Yacute => 'Ý',  # capital Y, acute accent

 aacute => 'á',  # small a, acute accent

 acirc  => 'â',  # small a, circumflex accent

 aelig  => 'æ',  # small ae diphthong (ligature)

 agrave => 'à',  # small a, grave accent

 aring  => 'å',  # small a, ring

 atilde => 'ã',  # small a, tilde

 auml   => 'ä',  # small a, dieresis or umlaut mark

 ccedil => 'ç',  # small c, cedilla

 eacute => 'é',  # small e, acute accent

 ecirc  => 'ê',  # small e, circumflex accent

 egrave => 'è',  # small e, grave accent

 eth    => 'ð',  # small eth, Icelandic

 euml   => 'ë',  # small e, dieresis or umlaut mark

 iacute => 'í',  # small i, acute accent

 icirc  => 'î',  # small i, circumflex accent

 igrave => 'ì',  # small i, grave accent

 iuml   => 'ï',  # small i, dieresis or umlaut mark

 ntilde => 'ñ',  # small n, tilde

 oacute => 'ó',  # small o, acute accent

 ocirc  => 'ô',  # small o, circumflex accent

 ograve => 'ò',  # small o, grave accent

 oslash => 'ø',  # small o, slash

 otilde => 'õ',  # small o, tilde

 ouml   => 'ö',  # small o, dieresis or umlaut mark

 szlig  => 'ß',  # small sharp s, German (sz ligature)

 thorn  => 'þ',  # small thorn, Icelandic

 uacute => 'ú',  # small u, acute accent

 ucirc  => 'û',  # small u, circumflex accent

 ugrave => 'ù',  # small u, grave accent

 uuml   => 'ü',  # small u, dieresis or umlaut mark

 yacute => 'ý',  # small y, acute accent

 yuml   => 'ÿ',  # small y, dieresis or umlaut mark

 # Some extra Latin 1 chars that are listed in the HTML3.2 draft (21-May-96)

 copy   => '©',  # copyright sign

 reg    => '®',  # registered sign

 nbsp   => "\240", # non breaking space

 # Additional ISO-8859/1 entities listed in rfc1866 (section 14)

 iexcl  => '¡',

 cent   => '¢',

 pound  => '£',

 curren => '¤',

 yen    => '¥',

 brvbar => '¦',

 sect   => '§',

 uml    => '¨',

 ordf   => 'ª',

 laquo  => '«',

'not'   => '¬',    # not is a keyword in perl

 shy    => '­',

 macr   => '¯',

 deg    => '°',

 plusmn => '±',

 sup1   => '¹',

 sup2   => '²',

 sup3   => '³',

 acute  => '´',

 micro  => 'µ',

 para   => '¶',

 middot => '·',

 cedil  => '¸',

 ordm   => 'º',

 raquo  => '»',

 frac14 => '¼',

 frac12 => '½',

 frac34 => '¾',

 iquest => '¿',

'times' => '×',    # times is a keyword in perl

 divide => '÷',

# some POD special entities

 verbar => '|',

 sol => '/'

);

##---------------------------------------------------------------------------

##---------------------------------

## Function definitions begin here

##---------------------------------

sub podchecker {

    my ($infile, $outfile, %options) = @_;

    local $_;

    ## Set defaults

    $infile  ||= \*STDIN;

    $outfile ||= \*STDERR;

    ## Now create a pod checker

    my $checker = new Pod::Checker(%options);

    ## Now check the pod document for errors

    $checker->parse_from_file($infile, $outfile);

    ## Return the number of errors found

    return $checker->num_errors();

}

##---------------------------------------------------------------------------

##-------------------------------

## Method definitions begin here

##-------------------------------

##################################

=over 4

=item C<Pod::Checker-E<gt>new( %options )>

Return a reference to a new Pod::Checker object that inherits from

Pod::Parser and is used for calling the required methods later. The

following options are recognized:

C<-warnings =E<gt> num>

  Print warnings if C<num> is true. The higher the value of C<num>,

the more warnings are printed. Currently there are only levels 1 and 2.

C<-quiet =E<gt> num>

  If C<num> is true, do not print any errors/warnings. This is useful

when Pod::Checker is used to munge POD code into plain text from within

POD formatters.

=cut

## sub new {

##     my $this = shift;

##     my $class = ref($this) || $this;

##     my %params = @_;

##     my $self = {%params};

##     bless $self, $class;

##     $self->initialize();

##     return $self;

## }

sub initialize {

    my $self = shift;

    ## Initialize number of errors, and setup an error function to

    ## increment this number and then print to the designated output.

    $self->{_NUM_ERRORS} = 0;

    $self->{_NUM_WARNINGS} = 0;

    $self->{-quiet} ||= 0;

    # set the error handling subroutine

    $self->errorsub($self->{-quiet} ? sub { 1; } : 'poderror');

    $self->{_commands} = 0; # total number of POD commands encountered

    $self->{_list_stack} = []; # stack for nested lists

    $self->{_have_begin} = ''; # stores =begin

    $self->{_links} = []; # stack for internal hyperlinks

    $self->{_nodes} = []; # stack for =head/=item nodes

    $self->{_index} = []; # text in X<>

    # print warnings?

    $self->{-warnings} = 1 unless(defined $self->{-warnings});

    $self->{_current_head1} = ''; # the current =head1 block

    $self->parseopts(-process_cut_cmd => 1, -warnings => $self->{-warnings});

}

##################################

=item C<$checker-E<gt>poderror( @args )>

=item C<$checker-E<gt>poderror( {%opts}, @args )>

Internal method for printing errors and warnings. If no options are

given, simply prints "@_". The following options are recognized and used

to form the output:

  -msg

A message to print prior to C<@args>.

  -line

The line number the error occurred in.

  -file

The file (name) the error occurred in.

  -severity

The error level, should be 'WARNING' or 'ERROR'.

=cut

# Invoked as $self->poderror( @args ), or $self->poderror( {%opts}, @args )

sub poderror {

    my $self = shift;

    my %opts = (ref $_[0]) ? %{shift()} : ();

    ## Retrieve options

    chomp( my $msg  = ($opts{-msg} || '')."@_" );

    my $line = (exists $opts{-line}) ? " at line $opts{-line}" : '';

    my $file = (exists $opts{-file}) ? " in file $opts{-file}" : '';

    unless (exists $opts{-severity}) {

       ## See if can find severity in message prefix

       $opts{-severity} = $1  if ( $msg =~ s/^\**\s*([A-Z]{3,}):\s+// );

    }

    my $severity = (exists $opts{-severity}) ? "*** $opts{-severity}: " : '';

    ## Increment error count and print message "

    ++($self->{_NUM_ERRORS})

        if(!%opts || ($opts{-severity} && $opts{-severity} eq 'ERROR'));

    ++($self->{_NUM_WARNINGS})

        if(!%opts || ($opts{-severity} && $opts{-severity} eq 'WARNING'));

    unless($self->{-quiet}) {

      my $out_fh = $self->output_handle() || \*STDERR;

      print $out_fh ($severity, $msg, $line, $file, "\n")

        if($self->{-warnings} || !%opts || $opts{-severity} ne 'WARNING');

    }

}

##################################

=item C<$checker-E<gt>num_errors()>

Set (if argument specified) and retrieve the number of errors found.

=cut

sub num_errors {

   return (@_ > 1) ? ($_[0]->{_NUM_ERRORS} = $_[1]) : $_[0]->{_NUM_ERRORS};

}

##################################

=item C<$checker-E<gt>num_warnings()>

Set (if argument specified) and retrieve the number of warnings found.

=cut

sub num_warnings {

   return (@_ > 1) ? ($_[0]->{_NUM_WARNINGS} = $_[1]) : $_[0]->{_NUM_WARNINGS};

}

##################################

=item C<$checker-E<gt>name()>

Set (if argument specified) and retrieve the canonical name of POD as

found in the C<=head1 NAME> section.

=cut

sub name {

    return (@_ > 1 && $_[1]) ?

        ($_[0]->{-name} = $_[1]) : $_[0]->{-name};

}

##################################

=item C<$checker-E<gt>node()>

Add (if argument specified) and retrieve the nodes (as defined by C<=headX>

and C<=item>) of the current POD. The nodes are returned in the order of

their occurrence. They consist of plain text, each piece of whitespace is

collapsed to a single blank.

=cut

sub node {

    my ($self,$text) = @_;

    if(defined $text) {

        $text =~ s/\s+$//s; # strip trailing whitespace

        $text =~ s/\s+/ /gs; # collapse whitespace

        # add node, order important!

        push(@{$self->{_nodes}}, $text);

        # keep also a uniqueness counter

        $self->{_unique_nodes}->{$text}++ if($text !~ /^\s*$/s);

        return $text;

    }

    @{$self->{_nodes}};

}

##################################

=item C<$checker-E<gt>idx()>

Add (if argument specified) and retrieve the index entries (as defined by

C<XE<lt>E<gt>>) of the current POD. They consist of plain text, each piece

of whitespace is collapsed to a single blank.

=cut

# set/return index entries of current POD

sub idx {

    my ($self,$text) = @_;

    if(defined $text) {

        $text =~ s/\s+$//s; # strip trailing whitespace

        $text =~ s/\s+/ /gs; # collapse whitespace

        # add node, order important!

        push(@{$self->{_index}}, $text);

        # keep also a uniqueness counter

        $self->{_unique_nodes}->{$text}++ if($text !~ /^\s*$/s);

        return $text;

    }

    @{$self->{_index}};

}

##################################

=item C<$checker-E<gt>hyperlink()>

Add (if argument specified) and retrieve the hyperlinks (as defined by

C<LE<lt>E<gt>>) of the current POD. They consist of a 2-item array: line

number and C<Pod::Hyperlink> object.

=back

=cut

# set/return hyperlinks of the current POD

sub hyperlink {

    my $self = shift;

    if($_[0]) {

        push(@{$self->{_links}}, $_[0]);

        return $_[0];

    }

    @{$self->{_links}};

}

## overrides for Pod::Parser

sub end_pod {

    ## Do some final checks and

    ## print the number of errors found

    my $self   = shift;

    my $infile = $self->input_file();

    if(@{$self->{_list_stack}}) {

        my $list;

        while(($list = $self->_close_list('EOF',$infile)) &&

          $list->indent() ne 'auto') {

            $self->poderror({ -line => 'EOF', -file => $infile,

                -severity => 'ERROR', -msg => '=over on line ' .

                $list->start() . ' without closing =back' });

        }

    }

    # check validity of document internal hyperlinks

    # first build the node names from the paragraph text

    my %nodes;

    foreach($self->node()) {

        $nodes{$_} = 1;

        if(/^(\S+)\s+\S/) {

            # we have more than one word. Use the first as a node, too.

            # This is used heavily in perlfunc.pod

            $nodes{$1} ||= 2; # derived node

        }

    }

    foreach($self->idx()) {

        $nodes{$_} = 3; # index node

    }

    foreach($self->hyperlink()) {

        my ($line,$link) = @$_;

        # _TODO_ what if there is a link to the page itself by the name,

        # e.g. in Tk::Pod : L<Tk::Pod/"DESCRIPTION">

        if($link->node() && !$link->page() && $link->type() ne 'hyperlink') {

            my $node = $self->_check_ptree($self->parse_text($link->node(),

                $line), $line, $infile, 'L');

            if($node && !$nodes{$node}) {

                $self->poderror({ -line => $line || '', -file => $infile,

                    -severity => 'ERROR',

                    -msg => "unresolved internal link '$node'"});

            }

        }

    }

    # check the internal nodes for uniqueness. This pertains to

    # =headX, =item and X<...>

    if($self->{-warnings} && $self->{-warnings}>1) {

      foreach(grep($self->{_unique_nodes}->{$_} > 1,

        keys %{$self->{_unique_nodes}})) {

          $self->poderror({ -line => '-', -file => $infile,

            -severity => 'WARNING',

            -msg => "multiple occurrence of link target '$_'"});

      }

    }

    # no POD found here

    $self->num_errors(-1) if($self->{_commands} == 0);

}

# check a POD command directive

sub command {

    my ($self, $cmd, $paragraph, $line_num, $pod_para) = @_;

    my ($file, $line) = $pod_para->file_line;

    ## Check the command syntax

    my $arg; # this will hold the command argument

    if (! $VALID_COMMANDS{$cmd}) {

       $self->poderror({ -line => $line, -file => $file, -severity => 'ERROR',

                         -msg => "Unknown command '$cmd'" });

    }

    else { # found a valid command

        $self->{_commands}++; # delete this line if below is enabled again

        ##### following check disabled due to strong request

        #if(!$self->{_commands}++ && $cmd !~ /^head/) {

        #    $self->poderror({ -line => $line, -file => $file,

        #         -severity => 'WARNING',

        #         -msg => "file does not start with =head" });

        #}

        # check syntax of particular command

        if($cmd eq 'over') {

            # check for argument

            $arg = $self->interpolate_and_check($paragraph, $line,$file);

            my $indent = 4; # default

            if($arg && $arg =~ /^\s*(\d+)\s*$/) {

                $indent = $1;

            }

            # start a new list

            $self->_open_list($indent,$line,$file);

        }

        elsif($cmd eq 'item') {

            # are we in a list?

            unless(@{$self->{_list_stack}}) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'ERROR',

                     -msg => '=item without previous =over' });

                # auto-open in case we encounter many more

                $self->_open_list('auto',$line,$file);

            }

            my $list = $self->{_list_stack}->[0];

            # check whether the previous item had some contents

            if(defined $self->{_list_item_contents} &&

              $self->{_list_item_contents} == 0) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'WARNING',

                     -msg => 'previous =item has no contents' });

            }

            if($list->{_has_par}) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'WARNING',

                     -msg => 'preceding non-item paragraph(s)' });

                delete $list->{_has_par};

            }

            # check for argument

            $arg = $self->interpolate_and_check($paragraph, $line, $file);

            if($arg && $arg =~ /(\S+)/) {

                $arg =~ s/[\s\n]+$//;

                my $type;

                if($arg =~ /^[*]\s*(\S*.*)/) {

                  $type = 'bullet';

                  $self->{_list_item_contents} = $1 ? 1 : 0;

                  $arg = $1;

                }

                elsif($arg =~ /^\d+\.?\s+(\S*)/) {

                  $type = 'number';

                  $self->{_list_item_contents} = $1 ? 1 : 0;

                  $arg = $1;

                }

                else {

                  $type = 'definition';

                  $self->{_list_item_contents} = 1;

                }

                my $first = $list->type();

                if($first && $first ne $type) {

                    $self->poderror({ -line => $line, -file => $file,

                       -severity => 'WARNING',

                       -msg => "=item type mismatch ('$first' vs. '$type')"});

                }

                else { # first item

                    $list->type($type);

                }

            }

            else {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'WARNING',

                     -msg => 'No argument for =item' });

                $arg = ' '; # empty

                $self->{_list_item_contents} = 0;

            }

            # add this item

            $list->item($arg);

            # remember this node

            $self->node($arg);

        }

        elsif($cmd eq 'back') {

            # check if we have an open list

            unless(@{$self->{_list_stack}}) {

                $self->poderror({ -line => $line, -file => $file,

                         -severity => 'ERROR',

                         -msg => '=back without previous =over' });

            }

            else {

                # check for spurious characters

                $arg = $self->interpolate_and_check($paragraph, $line,$file);

                if($arg && $arg =~ /\S/) {

                    $self->poderror({ -line => $line, -file => $file,

                         -severity => 'ERROR',

                         -msg => 'Spurious character(s) after =back' });

                }

                # close list

                my $list = $self->_close_list($line,$file);

                # check for empty lists

                if(!$list->item() && $self->{-warnings}) {

                    $self->poderror({ -line => $line, -file => $file,

                         -severity => 'WARNING',

                         -msg => 'No items in =over (at line ' .

                         $list->start() . ') / =back list'});

                }

            }

        }

        elsif($cmd =~ /^head(\d+)/) {

            my $hnum = $1;

            $self->{"_have_head_$hnum"}++; # count head types

            if($hnum > 1 && !$self->{'_have_head_'.($hnum -1)}) {

              $self->poderror({ -line => $line, -file => $file,

                   -severity => 'WARNING',

                   -msg => "=head$hnum without preceding higher level"});

            }

            # check whether the previous =head section had some contents

            if(defined $self->{_commands_in_head} &&

              $self->{_commands_in_head} == 0 &&

              defined $self->{_last_head} &&

              $self->{_last_head} >= $hnum) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'WARNING',

                     -msg => 'empty section in previous paragraph'});

            }

            $self->{_commands_in_head} = -1;

            $self->{_last_head} = $hnum;

            # check if there is an open list

            if(@{$self->{_list_stack}}) {

                my $list;

                while(($list = $self->_close_list($line,$file)) &&

                  $list->indent() ne 'auto') {

                    $self->poderror({ -line => $line, -file => $file,

                         -severity => 'ERROR',

                         -msg => '=over on line '. $list->start() .

                         " without closing =back (at $cmd)" });

                }

            }

            # remember this node

            $arg = $self->interpolate_and_check($paragraph, $line,$file);

            $arg =~ s/[\s\n]+$//s;

            $self->node($arg);

            unless(length($arg)) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'ERROR',

                     -msg => "empty =$cmd"});

            }

            if($cmd eq 'head1') {

                $self->{_current_head1} = $arg;

            } else {

                $self->{_current_head1} = '';

            }

        }

        elsif($cmd eq 'begin') {

            if($self->{_have_begin}) {

                # already have a begin

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'ERROR',

                     -msg => q{Nested =begin's (first at line } .

                     $self->{_have_begin} . ')'});

            }

            else {

                # check for argument

                $arg = $self->interpolate_and_check($paragraph, $line,$file);

                unless($arg && $arg =~ /(\S+)/) {

                    $self->poderror({ -line => $line, -file => $file,

                         -severity => 'ERROR',

                         -msg => 'No argument for =begin'});

                }

                # remember the =begin

                $self->{_have_begin} = "$line:$1";

            }

        }

        elsif($cmd eq 'end') {

            if($self->{_have_begin}) {

                # close the existing =begin

                $self->{_have_begin} = '';

                # check for spurious characters

                $arg = $self->interpolate_and_check($paragraph, $line,$file);

                # the closing argument is optional

                #if($arg && $arg =~ /\S/) {

                #    $self->poderror({ -line => $line, -file => $file,

                #         -severity => 'WARNING',

                #         -msg => "Spurious character(s) after =end" });

                #}

            }

            else {

                # don't have a matching =begin

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'ERROR',

                     -msg => '=end without =begin' });

            }

        }

        elsif($cmd eq 'for') {

            unless($paragraph =~ /\s*(\S+)\s*/) {

                $self->poderror({ -line => $line, -file => $file,

                     -severity => 'ERROR',

                     -msg => '=for without formatter specification' });

            }

            $arg = ''; # do not expand paragraph below