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