use HTML::Parser;

my $keyword = quotemeta 'match';

sub highlight {
	my $text = shift;
	$text =~ s|\b($keyword)\b|<span style="background: #FFFFFF">$1</span>|g;
	return $text;
}

my $html = q{
	<p id="match"><b>this is html match this</b><u value="don't match this">text html blah</u></p>
};

my $p = new HTML::Parser(api_version => 3, 
    handlers => {
        text=> [ sub { print highlight(shift) }, 'text'],
	default => [sub { print shift }, 'text'],
  });

$p->parse($html);