Description of EndpointAlias in URQ??

The "explanatory" text of the EndpointAlias element in the URQ message, contains the following sentence: "The E.164 address, if assigned, is required. " This sentence would seem to indicate that if I am unregistering, I always have to unregister the assigned E.164 address??? The sentence that follows, contradicts this: "Only values listed here are unregistered; this allows, for example, an H323_ID to be unregistered while leaving the E.164 address registered."

What is the intention of this sentence? Should I simply ignore it?

Frank