Queuing multiple command is implementation defined?

I just pay attention to this note of the OpenCL specification (1.0.48) :

Does it really means that second command queuing behavior is implementation dependent? :?

The behavior of multiple command-queues is not implementation defined. What this text is saying is that the behavior of context and command-queues is implementation defined if the device associated with the context / queue becomes unavailable. An example of a device becoming unavailable would be the device getting powered off.

Ok I’m relieved, I understood with that sentence:

It is possible that a device(s) becomes unavailable after a context and command-queues that use this device(s) have been created and commands have been queued to command-queues.

that a device can become unavailable because of its usage by command(s) queued…