tri5 chevy question?

the vent window on a convertible, the out front upright has two small tabs with hole in them, the holes cant be for screws other wise the screws would stick back through the trim outwards with the threads showing and be dangerous. So my Q is why are the two tabs there? and what do i do with them how does this piece of trim go on? (i did not take the car apart, nor do i have one to look at and the internet photos are not helpful.)