Special button that brings up a [PopupMenu] when clicked. Special button that brings up a [PopupMenu] when clicked. That's pretty much all it does, as it's just a helper class when building GUIs. Returns the [PopupMenu] contained in this button. If [code]true[/code], when the cursor hovers above another MenuButton within the same parent which also has [code]switch_on_hover[/code] enabled, it will close the current MenuButton and open the other one. Emitted when [PopupMenu] of this MenuButton is about to show.