PGPData

I am trying to interpret section "4.4.5 The PGPData Element" of the
dsig spec and it seems that -  without resorting to markup defined in
an external namespace - I am  restricted to including (in
PGPKeyPacket) only PGP packets of types specified in section 5.5 of
RFC 2440.

Am I right in thinking that this in turn means that I cannot include
signed key's in PGPData.PGPKeyPacket?

Regards
Tommy