function strip_multi_tags($str, $tag = 'div'){

     preg_match_all('/<'.$tag.'>|<\/'.$tag.'>/is', $str, $matched);

     $divs   = $matched[0];

     $pairs  = array();

     foreach($divs as $k => $v){

         if($v == '<'.$tag.'>'){

             $begin_keys[] = $k;

         } else {

             $bk = array_pop($begin_keys);

             if(!is_null($bk)){

                 $pairs[$bk] = $k;

             }

         }

     }

     $datas  = preg_split('/<'.$tag.'>|<\/'.$tag.'>/is', $str);

     $result = '';

     foreach($datas as $k => $v){

         if(isset($datas[$k+1]) && strlen(trim($datas[$k+1])) == 0

             && isset($pairs[$k]) && isset($pairs[$k+1])

             && ($k+1 + $pairs[$k+1]) == ($k + $pairs[$k]))

         {

             unset($divs[$k], $divs[$pairs[$k]]);

         }

         $result .= (strlen(trim($v))? $v: ''). (isset($divs[$k])? $divs[$k]: '');

     }

     return $result;

 }