* - a {@link ClientIdentifier}, which uniquely identifies a single instantiation of a particular frontend
* - an unsigned long, which uniquely identifies the history on the backend
* - an unsigned long cookie, assigned by the client and meaningless on the backend, which just reflects it back
* - a {@link ClientIdentifier}, which uniquely identifies a single instantiation of a particular frontend
* - an unsigned long, which uniquely identifies the history on the backend
* - an unsigned long cookie, assigned by the client and meaningless on the backend, which just reflects it back