True if the argument is a duration with the same or equivalent specification. Note that P1W equals P7D by definition, whereas e.g. P1M does not equal P30D since months are not 30 days in general. Less obvious, P1D is not equal to P24H in general.

Years are normalized to months, weeks to days and hours and minutes to seconds. After normalization, both durations are compared component by component. Iff all components match, this method returns true.