What is the relation between ViewRootImpl and DecorView?

[Android007]

As I understand, each Window on the client side (i.e. in the Activity process) has one ViewRootImpl that holds the hierarchy of its views.
The ViewRootImpl holds a single view called mView which is the first view of the hierarchy.
Each Window also has one DecorView which is supposed to be it's main view.
However I noticed that mView (in ViewRootImpl) is not DecorView as I expected, so I am puzzled...