Section 2.3 of eventing starts with:
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2.3 Notification Formats

This specification specifies two delivery formats: wrapped and unwrapped. Use of wrapped format indicates that notification messages MUST be contained in a wrapper element defined by this specification. Use of unwrapped format indicates that notification messages are not contained in a wrapper element. 
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We never really define what "format" means.  Sometimes formatting implies
things like encoding and that's not really what we're talking about here.

Proposal:
add an intro sentence that says something like:
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This specification does not mandate how events are serialized into
notification messages. Rather, within the Subscribe request message
a subscriber can specify a "Format" that indicates the set of rules
that MUST be followed when constructing notification messages.
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