In reply to kernalmode1:
#0 deferred assertions action blocks are scheduled for the Re-active region. Final deferred assertions action blocks are scheduled for the Postponed region. There are severe restrictions on what statements can execute in the postponed region (basically just messages)
The default clocking block input skew samples values in the postponed region of the previous time step. That value is the same as sampling in the preponed region of the current time step. There really is no difference between the two regions other than time has be updated to the next timestep. With a #0 skew, the input values are not “sampled”, they are whatever they are at the instant the clock event get triggered.