That's not quite the case either, because these things can be changed dynamically.

Furthermore, if an instance is linked with other instances using focus_next/previous, setting is_focusable of the widget to False, or disabled to True, should not modify focus_next/previous because at any moment it could become enabled again and we shouldn't have to change focus_next/previous every time it happens.

In fact, even if it's disabled, or is_focusable is False, when auto-populating, we still need include them, because they can become enabled. It's only in on_key_down that we skip disabled widgets.