It does not have to be fight or flight, exclusive, (in that you can only attack or defend or evade without any overlap) and it is not limited in direction or to a specific direction once started. And it is designed to allow solid, fight-stopping hits to be obtained from start to finish. It is a skill-set that makes use of instinctive reactions we all will have when faced with threat, but it is also complex and nuanced enough to be adaptable to a wide range of circumstances. The concepts and principles used are all combat-proven and continue to be.
And I don't know what else I can say about it, so I'll stop where I'm at.