Note: consider if the cross should be handled by an EventEmittingButton (from termbox) like thing.
So apparently OOUI sets tabindex="0" on the constraints icon, with that we can actually focus (and thus also handle blur). I'll do the same for us in order to re-implement the behavior as closely as possible.
I just implemented it like this, but I'm not sure that's going to suffice… if the user clicks on the popper, this will probably also trigger the blur and thus close the popper. Maybe if the popper is a direct child of the TaintedIcon <a> this will work, but I'm not sure.