Holds a compiled set of message registration information that
can be sent over the wire. The received message can then be
used to register all of the classes using the same IDs and
same ordering, etc.. The intent is that the server compiles
this message once it is sure that all serializable classes have
been registered. It can then send this to each new client and
they can use it to register all of the classes without requiring
exactly reproducing the same calls that the server did to register
messages.
Normally, JME recommends that apps have a common utility method
that they call on both client and server. However, this makes
pluggable services nearly impossible as some central class has to
know about all registered serializers. This message implementation
gets around by only requiring registration on the server.