RFC 2327 omissions and errors:

* "z=" omitted from zone-adjustments

* protocol on media-field is restricted to alpha-numeric,
  but example (RTP/AVP!) contains also "/"

* bwtype is restricted to alpha-numeric, but the RFC text discusses
  extensions like b=x-y:100

* att-field is restricted to alpha-numeric, but the RFC text discusses
  extensions like a=x-nokia-foo

* The BNF defintions "key-data" and "safe" are incomplete.