1. Set up a default handler (default_h) which has access to the tag name and unparsed HTML.
2. Set up a callback to look for table cells.
3. If you haven't found a table cell, spit out the unparsed HTML.
4. If you have found the start tag of a table cell, set a flag. You know any concurrent calls to your callback will be content within the table cell, until you hit a closing tag.

use HTML::Parser;

my $found = 0;

sub callback
{
    my($tagname, $text) = @_;
    
    if($tagname and $tagname eq 'td') {
        if(not $found) {
            # start tag.
            $found = 1;
        }
        else {
            # end tag.
            $found = 0;
        }
        return;
    }
    print $text and return unless $found;

    # If you're here, then the markup is within the td tags.
}

my $p = HTML::Parser->new(api_version => 3,
                          default_h => [\&callback,'tagname, text']);
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Hope this helps..