Standing Elbows

I know 12 to 6 elbows are banned on the ground but what about in stand up or clinch situations. I remember seeing a guy in The Contender: Muay Thai using them to good effect in one of those fights. They probably aren't as effective in MMA as you would have to be wary of getting taken down but are they illegal?

I have no idea what the official line on this is, but I'd imagine they are far less dangerous. Whilst standing in a clinch position it would be far more difficult to deliver a 12-6 elbow to a delicate area of the head like the temples. Generally standing strikes are less damaging than ground strikes in most cases, a lot more head movement and flexibility and no hard surface behind to add to the impact.