Implement 'whiteline_handler' attribute.

It is much like 'code_handler', 'cut_handler', and 'pod_handler',
except it is triggered on white lines. White lines are defined as
seemingly blank lines that match /[\t ]/.

Included is the updated code, documentation, and test cases.

lib/Pod/Simple.pm

@@ -93,13 +93,14 @@ __PACKAGE__->_accessorize(
  'codes_in_verbatim', # for PseudoPod extensions
 
  'code_handler',      # coderef to call when a code (non-pod) line is seen
- 'cut_handler',       # coderef to call when a =cut line is seen
- 'pod_handler',       # coderef to call when a =pod line is seen
+ 'cut_handler',       # ... when a =cut line is seen
+ 'pod_handler',       # ... when a =pod line is seen
+ 'whiteline_handler', # ... when a line with only whitespace is seen
  #Called like:
  # $code_handler->($line, $self->{'line_count'}, $self) if $code_handler;
  #  $cut_handler->($line, $self->{'line_count'}, $self) if $cut_handler;
  #  $pod_handler->($line, $self->{'line_count'}, $self) if $pod_handler;
-
+ #   $wl_handler->($line, $self->{'line_count'}, $self) if $wl_handler;
  'parse_empty_lists', # whether to acknowledge empty =over/=back blocks
 
 );

lib/Pod/Simple/BlackBox.pm

@@ -42,6 +42,7 @@ sub parse_lines {             # Usage: $parser->parse_lines(@lines)
 
   my $code_handler = $self->{'code_handler'};
   my $cut_handler  = $self->{'cut_handler'};
+  my $wl_handler   = $self->{'whiteline_handler'};
   $self->{'line_count'} ||= 0;
 
   my $scratch;
@@ -191,7 +192,12 @@ sub parse_lines {             # Usage: $parser->parse_lines(@lines)
       # TODO: add to docs: Note: this may cause cuts to be processed out
       #  of order relative to pods, but in order relative to code.
 
-    } elsif($line =~ m/^\s*$/s) {  # it's a blank line
+    } elsif($line =~ m/^(\s*)$/s) {  # it's a blank line
+      if (defined $1 and $1 =~ /[\t ]/) { # it's a white line
+        $wl_handler->(map $_, $line, $self->{'line_count'}, $self)
+          if $wl_handler;
+      }
+
       if(!$self->{'start_of_pod_block'} and @$paras and $paras->[-1][0] eq '~Verbatim') {
         DEBUG > 1 and print "Saving blank line at line ${$self}{'line_count'}\n";
         push @{$paras->[-1]}, $line;

lib/Pod/Simple/Subclassing.pod

@@ -826,6 +826,14 @@ This is just like the code_handler attribute, except that it's for
 unlikely to be interesting, but this is included for completeness.
 
 
+=item C<< $parser->whiteline_handler(  I<CODE_REF>  ) >>
+
+This is just like the code_handler attribute, except that it's for
+lines that are seemingly blank but have whitespace (" " and/or "\t") on them,
+not code lines. The same caveats apply. These lines are unlikely to be
+interesting, but this is included for completeness.
+
+
 =item C<< $parser->whine( I<linenumber>, I<complaint string> ) >>
 
 This notes a problem in the Pod, which will be reported to in the "Pod

t/cbacks.t

@@ -43,18 +43,20 @@ while(@from) {
     sub {
      $_[0]->code_handler(sub { $more .= $_[1] . ":" . $_[0] . "\n"       } );
      $_[0]->cut_handler( sub { $more .= "~" . $_[1] . ":" .  $_[0]. "\n" } );
-     $_[0]->pod_handler( sub { $more .= "~" . $_[1] . ":" .  $_[0]. "\n" } );
+     $_[0]->pod_handler( sub { $more .= "+" . $_[1] . ":" .  $_[0]. "\n" } );
+     $_[0]->whiteline_handler( 
+                         sub { $more .= "=" . $_[1] . ":" .  $_[0]. "\n" } );
     } => join "\n",
-    "",
+    " ", # space outside pod
     "\t# This is handy...",
     "=pod text",
-    "",
+    "\t", # tab inside pod
     "=cut more text",
-    "",
+    "\t", # tab outside pod
     "=pod",
-    "",
+    " \t ", # spaces and tabs inside pod
     "=head1 I  LIKE   PIE",
-    "",
+    " ", # space inside pod
     "=cut",
     "use Test::Harness;",
     "runtests(sort glob 't/*.t');",
@@ -69,12 +71,15 @@ while(@from) {
   }
 
   ok scalar($got = $more), scalar($exp = join "\n" =>
-   "1:",
+   "1: ",
    "2:\t# This is handy...",
-   "~3:=pod text",
+   "=4:\t",
+   "+3:=pod text",
    "~5:=cut more text",
-   "6:",
-   "~7:=pod",
+   "6:\t",
+   "=8: \t ",
+   "+7:=pod",
+   "=10: ",
    "~11:=cut",
    "12:use Test::Harness;",
    "13:runtests(sort glob 't/*.t');",