Newbie Question

Hi, I'm just getting into DBA and I have a question. I'm sure it has been asked a million times, but here I go.

Two opposing elements that are in mutual flank contanct and not engaged in combat are considered to be overlapping each other. What does this mean for subsequent bounds? Can one of the elements leave on its next bound or must it turn to engage?

That's it for now, thanks a bunch.