BUT WHILE I'M ON A ROLL, let's show you what button 5 does. (If you didn't know, everything up to now was spamming button 3, which is my single target tank spam)

/cast !rend
/click MultiBarLeftButton5
/click MultiBarLeftButton6
/click MultiBarLeftButton7
/click MultiBarLeftButton10
Theoretically this means I should be casting rend when it's not up, and not casting it when the target is rended. It used to work that way with Flame Shock on shamans.
Then you see button 5 (if you refer to the exhibit in the reply above of my UI) is also Rend, then button 6 is Thunder Clap and button 7 is Cleave. I do this because my warrior has the talent from the other tree that makes thunder clap spread rend like thunder CLAPP.

So it would probably work better as a castsequence macro. But I'm just putting it out there.



Now I know what you're thinking and I don't like it one bit. You're wanting to know what MultiBarLeftButton10 is.

The truth is: No one knows for sure. When I hover over it, it's a Ruby Essence from the Oculus. I guess something worth macroing had been there at one point, but no more. I left it in anyway because, being a cowardly and superstitious lot, maybe the fact I have a broken button in there is why my click macro even works where others fail.

Best of luck!