UMLR — are Create messages aynch or synch, or doesn't it matter?

In 14.3.24, the textual definition of MessageSort is badly formatted, which needs to be fixed. Then it provides for messages of sorts synchCall, asynchCall, asynchSignal, createMessage, deleteMessage and reply.

So is a createMessage synchronous, or asynchronous, or can it be either? The semantics of CreateObjectAction say “The new object is returned as the value of the action” - which implies that synchronous ought to be a possibility. But chapter 14 appears silent on this topic.