[arg_def [package cmdr::parameter] p] The [package cmdr::parameter] instance whose validation failed. The error message will contain this parameter's type and label (flag in case of an option). [arg_def list code] A list of additional elements for the error code to throw. Should detail the internal name of the validation type triggering the error. [arg_def string type] A string holding a human-readable name for the validation type triggering the error. (Conversely to the [arg code], which is for machine-readability, i.e. trapping) [arg_def string x] The string value which failed the validation. [arg_def string context] Additional context to show in the message. Defaults to the empty string.