/**
  * Get field HTML
  *
  * @param mixed $options
  * @param mixed $db_fields
  * @param mixed $meta
  * @param array $field
  * @return string
  */
 public static function walk($options, $db_fields, $meta, $field)
 {
     switch ($field['field_type']) {
         case 'checkbox_list':
         case 'radio_list':
             return RWMB_Input_List_Field::walk($options, $db_fields, $meta, $field);
             break;
         case 'select_tree':
             return RWMB_Select_Tree_Field::walk($options, $db_fields, $meta, $field);
             break;
         case 'select_advanced':
             return RWMB_Select_Advanced_Field::walk($options, $db_fields, $meta, $field);
             break;
         case 'select':
         default:
             return RWMB_Select_Field::walk($options, $db_fields, $meta, $field);
             break;
     }
 }