PHP从XSD架构中搜索和检索nillable元素

Question

I need to search and retrieve nillable elements from an XSD scheme file. I tried treating the XSD scheme as a text file and iterating over the lines using "strpos" function with "nillable" to print the element line:

public function echo_nillables(){
   $handle = fopen("filename.xsd");
   if($handle){
      while (($line = fgets($handle)) !== false){
         if(strpos($line, "nillable"){
            echo $line;
         }
      }
   }
}

but the fgets seems to ignore the xsd scheme lines and handle them like blank lines, resulting nothing to be echoed. is there a workaround or any other way to do it? all I need is for the function to echo the nillable line/element. Thanks.