1 while s/<([^<]+?)>([^<]*?)<\/>/
   $_{$1}->{$2} ||= do {
      #TODO: Make sure $1 doesn't contains "::".
      my $func = $pkg . "::" . $1;
      #TODO: Make sure $func exists.
      no strict 'refs';
      $func->($2)
   }
/e;