BInding on just "mod"

[PandaWood]

I wanted to detect the presence of "Ctl/Command" and log the fact
So I use "keyup" and "keydown" - something like this
Mousetrap.bind('mod', function(_this) {
_this.ctrlPressed = false;
}, 'keyup');

But I don't get any events firing - I can't see any documentation clarifying this but I gather just checking for "mod" and nothing else isn't supported/expected?