In reply to amrit_verif_singh:
From Section 14.3 of the LRM:
The clocking_event designates a particular event to act as the clock for the clocking block. The timing used to drive and sample all other signals specified in a given clocking block is governed by its clocking event.
So if your clocking_event is a combination of two clocks, then the timing is based off of what triggered the event.