Move the 'entity body' TODO.
Add a content type check to the match algorithm.

We need to verify that the content type of the resource matches, iff
the author provides a content type as a `ct` parameter to the `ni` 
URI.
Bypass digest checks for `about:blank`.
Reformat lists to 4 spaces.
Widen bypass to all URLs with 'about' scheme.

No reason to list things like `about:srcdoc`, just accept all 
'about:' URLs as valid.
Stub out `iframe` element processing.

A lot of open questions here...
Regenerating draft.