Alright, I was reading over the curriculum over at YMAA and mentioned in sparring was an "empty door". I assume this is an opponent's defense area like knees, etc?
what was mentioned specifically was:
This is the final stage of short range sparring training. In this stage, a student trains in attacking and defending all of the empty doors. The student is allowed to use hooking and sweeping to destroy the opponent's root. Grabbing and Qin Na (or Chin Na) applications are also permitted whenever feasible. Wrestling is also allowed in this stage.
I'm pretty sure I understand this; and if I do, then it's what I naturally do anyways when sparring. But I've never seen it broken down in this manner. Can someone explain this "empty door" and "root" stuff in a simpler manner?