Creating a filter name based on text from a file's call back.

file_filter_name.php

<?php

  $filterName = Inflector::underscore($callback);

  // Avoid creating a 'file_default_display_display' filter name.
  if ($filterName == 'default_display') {
      $filterName = 'file_'.$filterName;
  } else {
      $filterName = 'file_'.$filterName.'_display';
  }