The former. The text between the opening and closing unknown tag is simply
passed on and rendered as if the unknown tag wasn't there.
Thank you for pointing out the ambiguity, I will clarify this in the spec.
> Both options will of course deeply confuse browsers trying to
> calculate byte offsets within a file.
Why? Perhaps your parser is too cavalier about throwing away information.
Mine always knows the current position of elements, its just cheaper to
avoid copying lots of text when you don't need to.
Dave