[amluto]

More generally, if you want to include a block of untrustworthy structured data in a protocol, it’s very much preferable to do so in a way that does not require inspecting the data in question to figure out where it ends and thus where the outer protocol resumes.

English is not immune. Think about “who’s on first” — there is no way to distinguish the untrustworthy name “who” from a grammatical part of the conversation.