$catreg = "^(<[A-Za-z0-9]+>)*<H1>(<[A-Za-z0-9]+>)*([A-Za-z0-9]+)";

$_="<a><b><H1><c><d>foo";

if ( m!$catreg! ) {
    print "Matched \$1:$1 \$2$2 \$3$3\n";
} else {
    print "No Match\n";
}