Let me just start by saying that the words "p  = A pointer to the root of a valid memory block or to null." is pretty much the sentence used for all the functions in this module. I copied it here.

Back to the question, I'd guess the word "valid" just means that it has to be an actual (existing) block of memory, and not some random address. Sure, If the block is not managed, but existing, then we are documenting this function as ignoring it.

However, If the passed pointer is just some random address, then are making no promises (regardless of actual behavior, it should be *considered* undefined).

That's my take on it anyways.