If Key/type = GlobalReference, the key represents a reference to a source that can be globally identified.
If Key/type = FragmentReference, the key represents a bookmark or a similar local identifier within its parent element as specified by the key that precedes this key.
In all other cases, the key references a model element of the same or another Asset Administration Shell. The name of the model element is explicitly listed.
The docstring of this attribute should be adapted accordingly
In the spec:
The docstring of this attribute should be adapted accordingly