Hmm. Fair point. It's entirely possible that it's not obvious and that the "law" is almost a "reminder" of sorts to not assume you're getting well-formed inputs.

I'm still skeptical that this is the case with Postel's Law, but I do see that it's possible to read it that way. I guess I could always go do some research to prove it one way or the other, but... nah.

And yes, "Parse, don't validate." is one of my absolute favorite maxims (good word choice, by the way; I would've struggled on choosing a word for it here).