Controls belong to a big hierarchy. What may be the reason to highlight only two levels of controls if, in practice, there might be ten or twenty levels in the hierarchy?
The pictures show what the double-highlighting is. The inner square is over the control of interest, whereas the circumscribing one is over its parent.
However, things suddenly change when you put the cursor over WPF applications, its (WPF’s) derivatives and HTML:
This is a rather typical case: we are seeing a button or a link and, at the same time, the topmost control is a text.
The same story in Metro UI applications:
Here it is seen even better:
and here too:
The name of the button is not ‘Permissions’ as we could think, the name is ‘Back’.
At the end, there is a brilliant example:
There are TWO things on top of the button! This is the out-of-the-box Mail application.