section 11.1 ("transferable public keys") and section 12.1 ("key structures") are duplicative
section 11.1 ("transferable public keys") and section 12.1 ("key structures") are duplicative, and they are slightly out of sync.
for example, 11.1 doesn't mention direct key signatures, but 12.1 does. 11.1 mentions the optional padding packet, but 12.1 does not.
12.1 goes into significantly more detail about the expectations for different versions of transferable public keys.
12.1 is also part of §12, which is titled "Enhanced Key Formats", but it's unclear what is "enhanced" about them, except perhaps compared to RFC1991 (the comparable section was named "Enhanced Key Formats" in RFC 2440).
I think these two sections should be combined together to make the document shorter and clearer.