Basically that means that whenever the documentation lists a whole element structure, the only thing you have to specify is the uuid.
E.g. the element in a element - for an updatePhone, you'd specify
...
instead of going into the details of directoryNumber. Of course, you could specify the whole directoryNumber element, but the XML parser on the CCM (which by the way appears to be using regexp matching and is not a real xml parser) would simply look for the uuid, and if it's not there, refuse to process the command.