"User agent must provide access to parent document."
- This sentence is not grammatically correct English. Possible
intended rendition: "Conforming user agents must provide access to
the parent document."
- Notwithstanding the grammatically error, it's unclear how access
must be provided. The rest of this section describes an interface for
accessing the parent document but does not use "must" or "require"
language, so it's unclear if that is the specific interface that MUST