In the following I will call a view whose parent is the Activity a "top level view".
If you have a panel with no daughter views, then it does not seem possible to drag another view to make it a daughter. However, if a panel already has daughters, you can drag other views to add them as daughters.
If the lowest top level view in a tree has daughters then you cannot drag any view from higher in the tree to the bottom of the tree and make it a top level view. It is always a daughter of the bottom top level view.
If you have a panel with no daughter views, then it does not seem possible to drag another view to make it a daughter. However, if a panel already has daughters, you can drag other views to add them as daughters.
If the lowest top level view in a tree has daughters then you cannot drag any view from higher in the tree to the bottom of the tree and make it a top level view. It is always a daughter of the bottom top level view.