[mytailorisrich]

Let's not argue semantics here. An arbitrary sequence of bytes is an opaque data type, it has no structure, no meaning, no assumption can be made, and it must simply be passed on as is because it can be anything.

That's why they write that it should be treated as opaque data. My point (and the point of the comment I was replying to) is that 'should' is perhaps too weak a word in the context because previous history. In any case for robustness it is a must to treat it that way.