Perl CGI.pm Module and Random EXPORT_TAGS Processing of LABEL Tag

I was tracking down missing HTML4 LABEL tags (semantic tags that improve usability by associating mouse clicks for text labels with form inputs) in CGI.pm scripts using the radio_group() function, and discovered something that merits a blog post in case other programmers run into the same problem …

Using the -no_xhtml directive to CGI.pm disables the LABEL tag, regardless of what EXPORT_TAGS you specify. So even if :standard, :all, or :html4 are specified, the LABEL tag is not emitted.

The :html4 EXPORT_TAG looks like this:

                ':html4'=>[qw/abbr acronym bdo col colgroup del fieldset iframe
                            ins label legend noframes noscript object optgroup Q
                            thead tbody tfoot/],

But the plot thickened as I continued testing, because even if you don’t use -no_xhtml, the following incorrect behavior occurs …

CGI.pm has several EXPORT_TAGS, such as :html2, :html3 and :html4 that should restrict the available HTML tags according to the HTML version you want. However, LABEL, which appeared in HTML4 and is correctly defined only in the :html4 tag, is always displayed around radio_groups, etc.

Then I noticed CGI.pm conditional code like this:

    return $XHTML ? CGI::label(qq{<input type="checkbox" name="$name" value="$value"
             $tabindex$checked$other/>$the_label})
                  : qq{<input type="checkbox" name="$name" value="$value"
                    $checked$other>$the_label};

and

        if ($XHTML) {
           push @elements,
              CGI::label(
                   qq(<input type="$box_type" name="$name" value="$_"
                   $checkit$other$tab$attribs$disable/>$label)).${break};
        } else {
            push(@elements,qq/<input type="$box_type" name="$name" value="$_"
            $checkit$other$tab$attribs$disable>${label}${break}/);
        }

I don’t see why XHTML mode is needed for a HTML4 tag like LABEL. And if :html2 or :html3 is specified, LABEL should not be emitted.

At this point, I would have to question all of the XHTML-related code that was added to CGI.pm since 2.67. See changelog.

Another bug is that there should be a space before $checked above, so that the literal ‘checked’ becomes ‘ checked’.

Test script:

use CGI qw / -no_xhtml :html4 :form /;
#use CGI qw / :html4 :form /;

print 'Perl version: ', $], ', ', '$CGI::VERSION: ', $CGI::VERSION, "\n";

print radio_group(
                  -name=>'how far',
                  -values=>['10 ft','1 mile','10 miles','real far'],
                  -default=>'1 mile',
);

print "\n",
      bdo("HTML4 BDO tag"),
      "\n";

The output incorrectly omits LABEL tags.

Tested with Perl 5.8.5 (CGI.pm 3.29) and 5.8.8.