FE/BE docs and unsigned integers

The documentation doesn't give much of a hint that the protocol is using
unsigned integers. For instance, under ParameterDescription here:

http://www.postgresql.org/docs/9.3/static/protocol-message-formats.html

it says that the object ID is an Int32, which is described here:

http://www.postgresql.org/docs/9.3/static/protocol-message-types.html

as just a plain 32-bit integer. But the code (e.g.
getParamDescriptions()) is clearly reading it into an Oid, which is
unsigned.

Is there a reason this isn't clear? Is it meant to be ambiguous because
(as far as the protocol is concerned) it's just an opaque 32 bits?

It seems like it's worth a note somewhere at least.

Regards,
    Jeff Davis