PHP filter html tag attribute class (source code attached)

/**HTML Attribute Filter
* Date: 2013-09-22
* Author: fdipzone
* ver: 1.0
* edit: bbs.it-home.org
* Func:
* public strip filter attribute
* public setAllow set allowed Attributes
* public setException Set special case
* public setIgnore Set ignored mark
* private findElements Search for elements that need to be processed
* private findAttributes Search for attributes
* private removeAttributes Remove attributes
* private isException Determine whether it is a special case
* private createAttributes Create attributes
* private protect special character escape
*/

class HtmlAttributeFilter{ // class start

 private $_str = ''; // Source string
 private $_allow = array(); // Allowed reserved attributes such as: array('id','class','title')
 private $_exception = array(); // Special cases such as: array('a'=>array ('href','class'),'span'=>array('class'))
 private $_ignore = array(); // Ignore filtered tags. For example: array('span','img')

 /**Process HTML, filter unretained attributes
 * @param String $str source string
 * @return String
*/
 public function strip($str){
 $this->_str = $str;

 if(is_string($this->_str) && strlen($this-> ;_str)>0){ // Determine the string

 $this->_str = strtolower($this->_str); // Convert to lowercase

 $res = $this->findElements() ;
 if(is_string($res)){
 return $res;
 }
 $nodes = $this->findAttributes($res);
 $this->removeAttributes($nodes);
 }

 return $this->_str;
 }

 /**Set allowed properties
 * @param Array $param
*/
 public function setAllow($param=array()){
 $this->_allow = $param;
 }

 /** Set special case
 * @param Array $param
*/
 public function setException($param=array()){
 $this->_exception = $param;
 }

 /**Set ignored tags
 * @param Array $param
*/
 public function setIgnore($param=array ()){
 $this->_ignore = $param;
 }

 /**Search for elements to be processed*/
 private function findElements(){
 $nodes = array();
 preg_match_all("/<( [^ !/>n]+)([^>]*)>/i", $this->_str, $elements);
 foreach($elements[1] as $el_key => $ element){
 if($elements[2][$el_key]){
 $literal = $elements[0][$el_key];
 $element_name = $elements[1][$el_key];
 $attributes = $ elements[2][$el_key];
 if(is_array($this->_ignore) && !in_array($element_name, $this->_ignore)){
 $nodes[] = array('literal'=> ;$literal, 'name'=>$element_name, 'attributes'=>$attributes);
 }
 }
 }

 if(!$nodes[0]){
 return $this->_str;
 }else{
 return $nodes;
 }
 }


 /**Search attribute
 * @param Array $nodes elements to be processed
*/
 private function findAttributes($nodes){
 foreach($nodes as &$node){
 preg_match_all("/( [^ =]+)s*=s*["|']{0,1}([^"']*)["|']{0,1}/i", $node['attributes'] , $attributes);
 if($attributes[1]){
 foreach($attributes[1] as $att_key=>$att){
 $literal = $attributes[0][$att_key];
 $attribute_name = $attributes[1][$att_key];
 $value = $attributes[2][$att_key];
 $atts[] = array('literal'=>$literal, 'name'=>$attribute_name , 'value'=>$value);
 }
 }else{
 $node['attributes'] = null;
 }
 $node['attributes'] = $atts;
 unset($atts);
 }
 return $nodes;
 }

    /**Remove attributes
 * @param Array $nodes elements to be processed
*/
    private function removeAttributes($nodes){
        foreach($nodes as $node){
            $node_name = $node['name'];
            $new_attributes = '';
            if(is_array($node['attributes'])){
                foreach($node['attributes'] as $attribute){
                    if((is_array($this->_allow) && in_array($attribute['name'], $this->_allow)) || $this->isException($node_name, $attribute['name'], $this->_exception)){
                        $new_attributes = $this->createAttributes($new_attributes, $attribute['name'], $attribute['value']);
                    }
                }
            }
            $replacement = ($new_attributes) ? "<$node_name $new_attributes>" : "<$node_name>";
            $this->_str = preg_replace('/'.$this->protect($node['literal']).'/', $replacement, $this->_str);
        }
    }

    /**Determine whether it is a special case
 * @param String $element_name element name
 * @param String $attribute_name attribute name
 * @param Array $exceptions allowed special cases
 * @return boolean
*/
    private function isException($element_name, $attribute_name, $exceptions){
        if(array_key_exists($element_name, $this->_exception)){
            if(in_array($attribute_name, $this->_exception[$element_name])){
                return true;
            }
        }
        return false;
    }
    /**创建属性
    * @param  String $new_attributes
    * @param  String $name
    * @param  String $value
    * @return String
*/
    private function createAttributes($new_attributes, $name, $value){
        if($new_attributes){
            $new_attributes .= " ";
        }
        $new_attributes .= "$name="$value"";
        return $new_attributes;
    }

    /**Special character escape
 * @param String $str source string
 * @return String
*/
    private function protect($str){
        $conversions = array(
            "^" => "^",
            "[" => "[",
            "." => ".",
            "$" => "$",
            "{" => "{",
            "*" => "*",
            "(" => "(",
            "\" => "\\",
            "/" => "/",
            "+" => "+",
            ")" => ")",
            "|" => "|",
            "?" => "?",
            "<" => "<",
            ">" => ">"
        );
        return strtr($str, $conversions);
    }

} // class end

?>

2, Demonstration example

require('HtmlAttributeFilter.class.php');

$str = 'yunalove< ;/a>want to knowYES< ;/strong>';

Attached, the source code download address of php filtering html tag attribute class