php 字符串关键词高亮

写了个查找字符串中的关键词，将其高亮，不知道有没有什么问题。

protected function madeHighlight( $data )
   {
       //多个关键词以空格隔开
       $keywords = explode(' ', $_REQUEST[ 'q' ]);
       foreach ( $data as &$str ) {
           foreach ( $keywords as $word ) {
               //关键词长度
               $wordLength = mb_strlen($word);
               $start = -1;
               //查找字符串中的所有出现关键词的位置
               while ( ( $pos = mb_strpos(strtolower($str[ 'title' ]), strtolower($word), $start + 1) ) !== false ) {
                   $hightLight = 'aa-' . mb_substr($str[ 'title' ], $pos, $wordLength) . '-aa';
                   //加上高亮代码之后的字符串
                   $newStr = mb_substr($str[ 'title' ], 0, $pos) . $hightLight . mb_substr($str[ 'title' ], $pos + $wordLength);
                   $str[ 'title' ] = $newStr ;
                   //从高亮的关键词之后继续查找关键词
                   $start = $pos + mb_strlen($hightLight);
               }
           }
       }
       return $data;
   }