I am trying to create a "quarterly" pager, and I understand that there isn't a "quarter" granularity in the contextual filter. That would be a feature request.

But at the same time, I don't understand the descriptive text in the filter dialogue:

Filter any Views node date field by a date argument, using any common ISO date/period format (i.e. YYYY, YYYY-MM, YYYY-MM-DD, YYYY-W99, YYYY-MM-DD--P3M, P90D, etc).

I don't see anywhere in the rest of the dialogue where I could specify these formats. I have searched the documentation. Could someone point me to the explanation of how to create a contextual date filter for a pager of "P90D?"