delete hetml comment

  $content = preg_replace("/<!--(.*?)-->/s", "", $content);
  $content = preg_replace("/[\x0d\x0a]+/", " ", $content);
  $content = preg_replace("/>\s{4,}</", "> <", $content);
 $content = preg_replace('/(["\'])\s+\/>/', '\1/>', $content);