...
The Variable is to be attached to the underlying phone system and is for use in advanced applications. These variables cease to exist when the call stops and are not accessible by other calls.
...
User Space Variable
The Variable is stored in a the user space database. System User space variables are global, visible to all other calls and continue to exist indefinitely.
...
The contents of the Value are interpreted as the name of a Channel Variable and the Channel Variables value is copied to this Variable.
...
User Space Variable
The contents of the Value are interpreted as the name of a System User Space Variable and the System User Space Variables value is copied to this Variable.
Value
The value the Variable is to be set to. How this field is interpreted is dependent on the Value Variable Type.