In php projects, often use to label some filtering regular expressions, collections for spare:
$str=preg_replace("/\s+/", " ", $str); //Filter redundant Enter
$str=preg_replace("/<[ ]+/si","<",$str); //Filter <__(after "<" there is space)
$str=preg_replace("/<\!–.*?–>/si","",$str); //Note
$str=preg_replace("/<(\!.*?)>/si","",$str); //Filter DOCTYPE
$str=preg_replace("/<(\/?html.*?)>/si","",$str); //Filter html tag
$str=preg_replace("/<(\/?head.*?)>/si","",$str); //Filter head tag
$str=preg_replace("/<(\/?meta.*?)>/si","",$str); //Filter meta tag
$str=preg_replace("/<(\/?body.*?)>/si","",$str); //Filter body tag
$str=preg_replace("/<(\/?link.*?)>/si","",$str); //Filter link tag
$str=preg_replace("/<(\/?form.*?)>/si","",$str); //Filter form tag
$str=preg_replace("/cookie/si","COOKIE",$str); //Filter COOKIE tag
$str=preg_replace("/<(applet.*?)>(.*?)<(\/applet.*?)>/si","",$str); //Filter applet tag
$str=preg_replace("/<(\/?applet.*?)>/si","",$str); //Filter applet tag
$str=preg_replace("/<(style.*?)>(.*?)<(\/style.*?)>/si","",$str); //Filter style tag
$str=preg_replace("/<(\/?style.*?)>/si","",$str); //Filter style tag
$str=preg_replace("/<(title.*?)>(.*?)<(\/title.*?)>/si","",$str); //Filter title tag
$str=preg_replace("/<(\/?title.*?)>/si","",$str); //Filter title tag
$str=preg_replace("/<(object.*?)>(.*?)<(\/object.*?)>/si","",$str); //Filter object tag
$str=preg_replace("/<(\/?objec.*?)>/si","",$str); //Filter object tag
$str=preg_replace("/<(noframes.*?)>(.*?)<(\/noframes.*?)>/si","",$str); //Filter noframes tag
$str=preg_replace("/<(\/?noframes.*?)>/si","",$str); //Filter noframes tag
$str=preg_replace("/<(i?frame.*?)>(.*?)<(\/i?frame.*?)>/si","",$str); //Filter frame tag
$str=preg_replace("/<(\/?i?frame.*?)>/si","",$str); //Filter frame tag
$str=preg_replace("/<(script.*?)>(.*?)<(\/script.*?)>/si","",$str); //Filter script tag
$str=preg_replace("/<(\/?script.*?)>/si","",$str); //Filter script tag
$str=preg_replace("/javascript/si","javascript",$str); //Filter script tag
$str=preg_replace("/vbscript/si","Vbscript",$str); //Filter script tag
$str=preg_replace("/on([a-z]+)\s*=/si","On\\1=",$str); //Filter script tag
$str=preg_replace("/&#/si","&#",$str); //Filter script tag