Diff of /inc/Pod/Checker.pm [000000] .. [e362d3] Maximize Restore

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+#############################################################################
+# Pod/Checker.pm -- check pod documents for syntax errors
+#
+# Added =ff and O<> to Checker.pm to make bookchecker program
+# work for PDL::Book pod files.  Chris Marshall, 22-Jan-2012
+#
+# 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,
+    'ff'       =>  1,  # from pod2pdf
+);
+
+my %VALID_SEQUENCES = (
+    'I'  =>  1,
+    'B'  =>  1,
+    'S'  =>  1,
+    'C'  =>  1,
+    'L'  =>  1,
+    'F'  =>  1,
+    'X'  =>  1,
+    'Z'  =>  1,
+    'E'  =>  1,
+    'O'  =>  1,  # from pod2pdf
+);
+
+# 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  => '�',  # capital AE diphthong (ligature)
+ Aacute => '�',  # capital A, acute accent
+ Acirc  => '�',  # capital A, circumflex accent
+ Agrave => '�',  # capital A, grave accent
+ Aring  => '�',  # capital A, ring
+ Atilde => '�',  # capital A, tilde
+ Auml   => '�',  # capital A, dieresis or umlaut mark
+ Ccedil => '�',  # capital C, cedilla
+ ETH    => '�',  # capital Eth, Icelandic
+ Eacute => '�',  # capital E, acute accent
+ Ecirc  => '�',  # capital E, circumflex accent
+ Egrave => '�',  # capital E, grave accent
+ Euml   => '�',  # capital E, dieresis or umlaut mark
+ Iacute => '�',  # capital I, acute accent
+ Icirc  => '�',  # capital I, circumflex accent
+ Igrave => '�',  # capital I, grave accent
+ Iuml   => '�',  # capital I, dieresis or umlaut mark
+ Ntilde => '�',  # capital N, tilde
+ Oacute => '�',  # capital O, acute accent
+ Ocirc  => '�',  # capital O, circumflex accent
+ Ograve => '�',  # capital O, grave accent
+ Oslash => '�',  # capital O, slash
+ Otilde => '�',  # capital O, tilde
+ Ouml   => '�',  # capital O, dieresis or umlaut mark
+ THORN  => '�',  # capital THORN, Icelandic
+ Uacute => '�',  # capital U, acute accent
+ Ucirc  => '�',  # capital U, circumflex accent
+ Ugrave => '�',  # capital U, grave accent
+ Uuml   => '�',  # capital U, dieresis or umlaut mark
+ Yacute => '�',  # capital Y, acute accent
+ aacute => '�',  # small a, acute accent
+ acirc  => '�',  # small a, circumflex accent
+ aelig  => '�',  # small ae diphthong (ligature)
+ agrave => '�',  # small a, grave accent
+ aring  => '�',  # small a, ring
+ atilde => '�',  # small a, tilde
+ auml   => '�',  # small a, dieresis or umlaut mark
+ ccedil => '�',  # small c, cedilla
+ eacute => '�',  # small e, acute accent
+ ecirc  => '�',  # small e, circumflex accent
+ egrave => '�',  # small e, grave accent
+ eth    => '�',  # small eth, Icelandic
+ euml   => '�',  # small e, dieresis or umlaut mark
+ iacute => '�',  # small i, acute accent
+ icirc  => '�',  # small i, circumflex accent
+ igrave => '�',  # small i, grave accent
+ iuml   => '�',  # small i, dieresis or umlaut mark
+ ntilde => '�',  # small n, tilde
+ oacute => '�',  # small o, acute accent
+ ocirc  => '�',  # small o, circumflex accent
+ ograve => '�',  # small o, grave accent
+ oslash => '�',  # small o, slash
+ otilde => '�',  # small o, tilde
+ ouml   => '�',  # small o, dieresis or umlaut mark
+ szlig  => '�',  # small sharp s, German (sz ligature)
+ thorn  => '�',  # small thorn, Icelandic
+ uacute => '�',  # small u, acute accent
+ ucirc  => '�',  # small u, circumflex accent
+ ugrave => '�',  # small u, grave accent
+ uuml   => '�',  # small u, dieresis or umlaut mark
+ yacute => '�',  # small y, acute accent
+ yuml   => '�',  # 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   => '�',
+ laquo  => '�',
+'not'   => '�',    # not is a keyword in perl
+ shy    => '�',
+ macr   => '�',
+ deg    => '�',
+ plusmn => '�',
+ sup1   => '�',
+ sup2   => '�',
+ sup3   => '�',
+ acute  => '�',
+ micro  => '�',
+ para   => '�',
+ middot => '�',
+ cedil  => '�',
+ ordm   => '�',
+ raquo  => '�',
+ frac14 => '�',
+ frac12 => '�',
+ frac34 => '�',
+ 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' });
+            }
+            $arg = ''; # do not expand paragraph below
+        }
+        elsif($cmd =~ /^(pod|cut)$/) {
+            # check for argument
+            $arg = $self->interpolate_and_check($paragraph, $line,$file);
+            if($arg && $arg =~ /(\S+)/) {
+                $self->poderror({ -line => $line, -file => $file,
+                      -severity => 'ERROR',
+                      -msg => "Spurious text after =$cmd"});
+            }
+        }
+    $self->{_commands_in_head}++;
+    ## Check the interior sequences in the command-text
+    $self->interpolate_and_check($paragraph, $line,$file)
+        unless(defined $arg);
+    }
+}
+
+sub _open_list
+{
+    my ($self,$indent,$line,$file) = @_;
+    my $list = Pod::List->new(
+           -indent => $indent,
+           -start => $line,
+           -file => $file);
+    unshift(@{$self->{_list_stack}}, $list);
+    undef $self->{_list_item_contents};
+    $list;
+}
+
+sub _close_list
+{
+    my ($self,$line,$file) = @_;
+    my $list = shift(@{$self->{_list_stack}});
+    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' });
+    }
+    undef $self->{_list_item_contents};
+    $list;
+}
+
+# process a block of some text
+sub interpolate_and_check {
+    my ($self, $paragraph, $line, $file) = @_;
+    ## Check the interior sequences in the command-text
+    # and return the text
+    $self->_check_ptree(
+        $self->parse_text($paragraph,$line), $line, $file, '');
+}
+
+sub _check_ptree {
+    my ($self,$ptree,$line,$file,$nestlist) = @_;
+    local($_);
+    my $text = '';
+    # process each node in the parse tree
+    foreach(@$ptree) {
+        # regular text chunk
+        unless(ref) {
+            # count the unescaped angle brackets
+            # complain only when warning level is greater than 1
+            if($self->{-warnings} && $self->{-warnings}>1) {
+              my $count;
+              if($count = tr/<>/<>/) {
+                $self->poderror({ -line => $line, -file => $file,
+                     -severity => 'WARNING',
+                     -msg => "$count unescaped <> in paragraph" });
+                }
+            }
+            $text .= $_;
+            next;
+        }
+        # have an interior sequence
+        my $cmd = $_->cmd_name();
+        my $contents = $_->parse_tree();
+        ($file,$line) = $_->file_line();
+        # check for valid tag
+        if (! $VALID_SEQUENCES{$cmd}) {
+            $self->poderror({ -line => $line, -file => $file,
+                 -severity => 'ERROR',
+                 -msg => qq(Unknown interior-sequence '$cmd')});
+            # expand it anyway
+            $text .= $self->_check_ptree($contents, $line, $file, "$nestlist$cmd");
+            next;
+        }
+        if($nestlist =~ /$cmd/) {
+            $self->poderror({ -line => $line, -file => $file,
+                 -severity => 'WARNING',
+                 -msg => "nested commands $cmd<...$cmd<...>...>"});
+            # _TODO_ should we add the contents anyway?
+            # expand it anyway, see below
+        }
+        if($cmd eq 'E') {
+            # preserve entities
+            if(@$contents > 1 || ref $$contents[0] || $$contents[0] !~ /^\w+$/) {
+                $self->poderror({ -line => $line, -file => $file,
+                    -severity => 'ERROR',
+                    -msg => 'garbled entity ' . $_->raw_text()});
+                next;
+            }
+            my $ent = $$contents[0];
+            my $val;
+            if($ent =~ /^0x[0-9a-f]+$/i) {
+                # hexadec entity
+                $val = hex($ent);
+            }
+            elsif($ent =~ /^0\d+$/) {
+                # octal
+                $val = oct($ent);
+            }
+            elsif($ent =~ /^\d+$/) {
+                # numeric entity
+                $val = $ent;
+            }
+            if(defined $val) {
+                if($val>0 && $val<256) {
+                    $text .= chr($val);
+                }
+                else {
+                    $self->poderror({ -line => $line, -file => $file,
+                        -severity => 'ERROR',
+                        -msg => 'Entity number out of range ' . $_->raw_text()});
+                }
+            }
+            elsif($ENTITIES{$ent}) {
+                # known ISO entity
+                $text .= $ENTITIES{$ent};
+            }
+            else {
+                $self->poderror({ -line => $line, -file => $file,
+                    -severity => 'WARNING',
+                    -msg => 'Unknown entity ' . $_->raw_text()});
+                $text .= "E<$ent>";
+            }
+        }
+        elsif($cmd eq 'L') {
+            # try to parse the hyperlink
+            my $link = Pod::Hyperlink->new($contents->raw_text());
+            unless(defined $link) {
+                $self->poderror({ -line => $line, -file => $file,
+                    -severity => 'ERROR',
+                    -msg => 'malformed link ' . $_->raw_text() ." : $@"});
+                next;
+            }
+            $link->line($line); # remember line
+            if($self->{-warnings}) {
+                foreach my $w ($link->warning()) {
+                    $self->poderror({ -line => $line, -file => $file,
+                        -severity => 'WARNING',
+                        -msg => $w });
+                }
+            }
+            # check the link text
+            $text .= $self->_check_ptree($self->parse_text($link->text(),
+                $line), $line, $file, "$nestlist$cmd");
+            # remember link
+            $self->hyperlink([$line,$link]);
+        }
+        elsif($cmd =~ /[BCFIOS]/) {
+            # add the guts
+            $text .= $self->_check_ptree($contents, $line, $file, "$nestlist$cmd");
+        }
+        elsif($cmd eq 'Z') {
+            if(length($contents->raw_text())) {
+                $self->poderror({ -line => $line, -file => $file,
+                    -severity => 'ERROR',
+                    -msg => 'Nonempty Z<>'});
+            }
+        }
+        elsif($cmd eq 'X') {
+            my $idx = $self->_check_ptree($contents, $line, $file, "$nestlist$cmd");
+            if($idx =~ /^\s*$/s) {
+                $self->poderror({ -line => $line, -file => $file,
+                    -severity => 'ERROR',
+                    -msg => 'Empty X<>'});
+            }
+            else {
+                # remember this node
+                $self->idx($idx);
+            }
+        }
+        else {
+            # not reached
+            croak 'internal error';
+        }
+    }
+    $text;
+}
+
+# process a block of verbatim text
+sub verbatim {
+    ## Nothing particular to check
+    my ($self, $paragraph, $line_num, $pod_para) = @_;
+
+    $self->_preproc_par($paragraph);
+
+    if($self->{_current_head1} eq 'NAME') {
+        my ($file, $line) = $pod_para->file_line;
+        $self->poderror({ -line => $line, -file => $file,
+            -severity => 'WARNING',
+            -msg => 'Verbatim paragraph in NAME section' });
+    }
+}
+
+# process a block of regular text
+sub textblock {
+    my ($self, $paragraph, $line_num, $pod_para) = @_;
+    my ($file, $line) = $pod_para->file_line;
+
+    $self->_preproc_par($paragraph);
+
+    # skip this paragraph if in a =begin block
+    unless($self->{_have_begin}) {
+        my $block = $self->interpolate_and_check($paragraph, $line,$file);
+        if($self->{_current_head1} eq 'NAME') {
+            if($block =~ /^\s*(\S+?)\s*[,-]/) {
+                # this is the canonical name
+                $self->{-name} = $1 unless(defined $self->{-name});
+            }
+        }
+    }
+}
+
+sub _preproc_par
+{
+    my $self = shift;
+    $_[0] =~ s/[\s\n]+$//;
+    if($_[0]) {
+        $self->{_commands_in_head}++;
+        $self->{_list_item_contents}++ if(defined $self->{_list_item_contents});
+        if(@{$self->{_list_stack}} && !$self->{_list_stack}->[0]->item()) {
+            $self->{_list_stack}->[0]->{_has_par} = 1;
+        }
+    }
+}
+
+1;
+
+__END__
+
+=head1 AUTHOR
+
+Please report bugs using L<http://rt.cpan.org>.
+
+Brad Appleton E<lt>bradapp@enteract.comE<gt> (initial version),
+Marek Rouchal E<lt>marekr@cpan.orgE<gt>
+
+Based on code for B<Pod::Text::pod2text()> written by
+Tom Christiansen E<lt>tchrist@mox.perl.comE<gt>
+
+=cut
+