/**
  * Open an HTML tag for the given field.
  * Maps the name and id of the control so that it is uniformly available as JavaScript (automatically
  * mapping {@link ARRAY_FIELD}s). Also renders the field's enabled state.
  * @param FIELD $field
  * @param string $tag_name Name of the HTML tag to generate.
  * @param string $dom_id
  * @return string
  * @access private
  */
 protected function _start_control($field, $tag_name = 'input', $dom_id = null)
 {
     if (isset($dom_id)) {
         $id = $dom_id;
     } else {
         $id = $field->id;
     }
     $Result = '<' . $tag_name . ' name="' . $field->js_name() . '" id="' . $id . '"';
     if (!$field->enabled) {
         $Result .= ' disabled';
     }
     if ($field->required) {
         $Result .= ' required';
     }
     return $Result;
 }