I just spent a couple of hours prowling through the zigbee specification at zigbee.org. What a royal pain in the bottom it is getting documents and specifications. Net though, they don't specify stuff like:
How to turn the light on
How to turn the light off
How to check if the light is on
How to check if the door is open
etc.
They do specify the interaction of nodes, controllers, routing of messages and such. Basically, it's a network specification, with the specifics that most of us are interested in being left to the manufacturers. That means that digi zigbee devices will operate within their specification, but digi has only certified routers and controllers, since matching a particular manufacturers technique of actual control would mean the manufacturer would have to publish something to tell us how they do it.
I hold exactly zero expectations of a wall switch that will work with several manufacturer's controllers. There's just too much flex given in how to do such a thing. Where we worry about exactly how to send a signal to turn a light on and then check to make sure it is actually on, the zigbee spec. leaves that to the manufacturer to implement any way they want to.
Strangely, that means that my NETWORK is zigbee compliant, but my devices don't match any manufacturers' simply because I use the zigbee protocol in the various modems.
sigh....
PS, someone out there tell me I'm wrong.....please.