code: func URL(req *http.Request, userStruct FieldMapper) error {
  	err := urlBinder(req, userStruct)
  	if len(err) > 0 {
  		return err
  	}
  	return nil
  
  }
docs: // URL reads data out of the query string into a struct you provide.
  // This function invokes data validation after deserialization.