function booboo($content)
{
  if (stristr('<!--blah-->', $content))
    {
    	$content = preg_replace_callback('|<!--blah-->|i', 'foobar', $content);
  	}
  elseif (stristr('<p><!--blah--></p>', $content))
    {
    	$content = preg_replace_callback('|<p><!--blah--></p>|i', 'foobar', $content);
  	}
  return $content;
}