As far as I know, RightDown (and RightUp) is not yet in the API.
My goal was to provide an easy way to create a form button like we always seen. Just look at the "submit reply" button below the post form.
Press, and keep it pressed. You can still change advice until you release.
When you click on the close button on the top left (may depend on your OS and theme), that's the same. So I wanted to keep my customs
So, this is typically a form button, rather than an ability one, although I'm sure - I never really paid attention to it - this is the same case.
If you still want your button to fire instantly, then you can customize the function.
Note that we don't yet have the complete API, and we have no idea on the programming level. Right now, we got GUI basics, and we can do some stuff with. But I think they may provide us button, textarea, scrollbars and so on... We could do this with a few more primitives to handle keyboard input and mouse move (in fact, mouseover and mouseout would be enough !), but this will be CPU hungry, where native would be far more efficient I guess.
So, keep having a look at each patch. I don't know if they're gonna update the pastebin, but I will refresh everyday.
Right now, it's a thumbnail, more than the real API, and nothing is certain about what we might be able to do, and how.