WPF Popup hiding problem

Question

Suppose you have a ToggleButton for opening a Popup, same behaviour as all known elements as ComboBox etc.

... which is this c

Answer 1

To prevent closing the Popup by clicking its background, insert something that will fill it.

In this example, clicking the unfilled space will close the Popup:

In this example, clicking the unfilled space will NOT close the Popup: