brew on Linux should know nothing about casks

[RalphCorderoy]

I used brew to search for arduino and saw it was a cask. Not knowing what they were, I spent time reading about them. I then waited for the tapping of the cask which was a large download. Only then, when I tried to install the arduino cask, did I find out they're not supported on Linux. I then how to find out how to not tap that useless formula repo; it's untap, which isn't mentioned in brew help tap's output.

All of that time would have been saved if brew on Linux didn't know about casks, or at least preceded anything to do with them with a warning they're of no use.