MODX OnPageNotFound

<?php
if($modx->event->name=="OnPageNotFound"){
$alias = $modx->context->getOption('request_param_alias', 'q');
if (!isset($_REQUEST[$alias])) {return false;}
$request = $_REQUEST[$alias];
$url=strtr($request,array('model/'.$_GET['md'].'/'=>''));
if (!$section = $modx->findResource($url))  return false;
$modx->sendForward($section);
}