You can use this as a base class for your widgets instead of User Widget, in order to optionally get some automatic focus behaviour.
Checking the "Enable Automatic Focus" box opts into this behaviour, and whenever this widget is added to the viewport it will automatically be given focus if its priority is equal or higher to anything else on screen right now. You set the "Automatic Focus Priority" member to a value and the highest wins.
When a widget with auto focus enabled is removed from the viewport while it has the focus, it triggers the focus system to automatically give focus to the highest priority widget still in the viewport.
This makes it easier to make UIs with several independent elements, which can supersede each other, but you need to have a reliable focus chain. By enabling this option on all your dialogs (it's automatically enabled on Menus) and setting priorities accordingly, you can ensure that focus is reliably transferred without having to do it manually in all combinations of sequences.
Focus is given by calling the SetFocusProperly method. Some subclasses like
Focusable Panel automatically override this to give focus
to a child widget, but you can override it to do whatever you like (default is
just to call SetFocus on self). The reason for using SetFocusProperly is that SetFocus
isn't virtual in the Unreal base classes 🙄