Strip non-tags

Hi,
Is there a quick way to do the reverse of what strip_tags function does.

I mean, strip_tags strips all tags from a string and returns the remaining, what I need is a function that strips all strings that are not tags and leave just tags.

 

preg_match_all('/<(.*?)>/',$html,$tags);
foreach ($tags[0] as $x)
      print $x;

PHP:

untested, but should work.