Project 4 - Stack, op=11?

In the assignment of designing stacks, do we have to worry about what happens if op=11? Or we can assume it’s never gonna be entered as an input?
Should we set op=00 if op=11?

op=11 is not part of the specification.

So does this mean we can ignore that option and assume it’s never going to be entered as an input? Is it okay to set op=00 in case op=11?