Comment 50 for bug 261573

For the part about it working "out of the box"... Just for informational purposes.. There have been arguments against the sort of thing you suggest as well. For instance. There is no Num Lock key on Apple keyboards, but the Clear Key (which is in he same location on the Full Keyboards) is mapped to NumLock instead. Apple keyboards also do not have arrow keys on the numpads, so it is strange to the user when they work as arrow keys, then there is no key marked to switch that function. Point being, If the key doesn't exist on the keyboard already, you have to be careful changing the marked function of keys already on the keyboard. Otherwise I agree that the small enter key would be a good choice for conversion to AltGr.

So how does it function in OSX? How would to get the @? Maybe that would be a good choice to mimick...

Also, from what I read above, you only talked about the Compose Key Options... There are other options as well. The third level chooser options should allow you to set an existing key to do what you want.