Unless it's essential they're screwed, I'd use bolts through the shelf when you come to fit them. One of the round tuit jobs here is to fix the drop front on my wife's bureau - veneered chipboard. It's a horrible thing which I've had a go at before, but the chipboard is so weak it's impossible to get a fixing nicely.
If it shows and you're veneering the non-hinge side (bottom when it's open), might you embed a nut in that side (which you can run a bolt into through from the stay side), so that it's invisible once veneered?
Personally I hate the things. Lopers are a much nicer solution, and there even used to be an 'automatic' mechanism for them, which pushed them out when the fall flap was opened (wife's grandfather's fall-front had them). But I guess this isn't a writing desk...
It's in neither my Chambers' nor the Concise Oxford dictionary, and Alan Peters' revision of Joyce doesn't mention it (but then he doesn't discuss it, either, preferring metal stays).
It is discussed in Illustrated Cabinetmaking (Bill Hylton/American Woodworker, p.207), but that's all about design (Joyce is 50% technique). Frustratingly, one of the offspring has 'borrowed' my American dictionary, so I can't check that.
Anyway, it's one of the two sliding-out supports either side of the top drawer of a fall-front writing desk (or similar).