That would mean 3 implementations, 3 interfaces 2 parsers.
The "jboss" one in fact just extends the spec one and I think that is the one the "integration code" should use in AS7.
We have:
web.xml -> spec (parser/implementation/interface)
jboss-web.xml -> jboss (parser/implementation/interface)
merging (spec + jboss + annotations) would use the jboss created by the parsing of jboss-web.xml or a default configuration.