Ostensibly, the can_use block should be a way to define who can and can't use the CB. But what does it actually do? Well, it doesn't prevent the CB from appearing if it evaluates to false, that's actually what can_use_title does. If can_use evaluates to false but can_use_title does not, the CB appears and can be selected, but the game confusingly tells you you haven't selected a CB. This is strictly worse than can_use_gui, which also doesn't prevent the CB from showing up under any circumstances, but it does show you the tooltips for all the conditions that have to be satisfied in order for you to use the CB. So what reason is there to put any conditions in can_use, rather than putting them all in can_use_gui, where they will actually present a user-friendly interface? Even if the condition doesn't have a nice tooltip, you can fix that with custom_tooltip. I'm just not seeing that there's any real use case for the can_use block. On top of this, what is actually the scope at the top level of the can_use block? It's not ROOT, that's for sure. I guess it is a mystery?