Filter content with html tags

For details, please refer to
Zhou Xiaoshe’s Secret Garden---- PHP Handwriting Method for Filtering HTML Characters
http://zhousir.net/php-html-filtering-method-handwritten-characters.html

function html2text($str){
 $str = trim($str);
 $str = preg_replace("/||/isU","" ,$str);
 $alltext = "";
 $start = 1;
 for($i=0;$i31){
 $alltext .= $str[$i];
 }
 }
 }
 $ alltext = str_replace("　"," ",$alltext);
 $alltext = preg_replace("/&([^;&]*)(;|&)/","",$alltext);
 $alltext = preg_replace("/[ ]+/s"," ",$alltext);
 $alltext = htmlspecialchars($alltext,ENT_QUOTES);
 return $alltext;
}