The idsubdatatable Property

Please find attached the properties of an object that I recently created with the Events.getCategory() method. Notice the presence of the idsubdatatable property and its value.

According to the manual subdatatables are tables that related to specific or even all rows of a datatable. Now, I have taught myself how to use bulk requests, and for each array that is returned the several objects contained within each contains a idsubdatatable property with a unique value…

Further, a close examination of the Events API contains the following passage:

The Events.get* reports can be used with an optional &secondaryDimension parameter. Secondary dimension is the dimension used in the sub-table of the Event report you are requesting.

QUESTIONS: Is there any relationship between the two subtables? If so, what is it, and how do I access them to see what is contained within?

Roddyidsubdatatable_property