This addon is smart.
But i will try to explain how it thinks:
The addon will check first what parent both the start and the stop block have.
Then it adds a start and a stop element in this parent. This way it knows where to start and stop.
It then selects all elements between the newly added start and stop elements, en wraps them.
This includes the start and stop blocks you placed!
It then removes the newly added elements (no need to be messy).
Becouse of this approach, we are able to enable you to place the wrap-anything blocks on any location. And the addon will still function.