+ datetime.timedelta representing the duration described.
+ This uses `datetime_utils.parse_duration` to parse durations
+ and expects data such as:
+
+ - 15 days, 3 hours, 15 minutes
+ - 15 days 3 hours 15 minutes
+ - 15d 3h 15m
+ - 15d3h5m
+ - 3m 2s
+ - 1000s
+
+ If the duration is not parsable, raise an ArgumentTypeError.
+
+ Args:
+ txt: data passed to a commandline arg expecting a duration.
+
+ Returns:
+ The datetime.timedelta described by txt or raises ArgumentTypeError
+ on error.
+