So when did "incidental facemasking" become legal?

[Raptorman]

So then how does the conversation go?

Line Judge throws flag.

Ref: "Hey, what's the call?"
LJ: "Facemask."
Ref: "I didn't see any facemasking."
LJ: "I did. He hooked it and didn't let go. That's why I threw the flag."
Ref: "Hmm... I'm going to allow this."

Like I said, I have seen it before. Don't necessarily agree with it, but it was not the first time I have seen them not penalize someone for it. I also don't understand that if it's not a facemask, why is it not an "illegal hands to the face" call? One of those judgment calls we fans will never understand.