PHP filters the BOM of implementation code in the PHP page

function checkBOM ($filename) {
       $contents = file_get_contents($filename);
       $charset[1] = substr($contents, 0, 1);
       $charset[2] = substr($contents, 1, 1);
      $charset[3] = substr($contents, 2, 1);
      if (ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191) {
               $rest = substr($contents, 3);
               rewrite $rest;
      }else{
　　　　　　return false;
　　　 }
 }