I think it's ok that `:wifth => 50` does not raise an error as the option is just ignored, but silently swallowing `:width => "50$"` and `.width = "50$"` but maybe we should move this discussion to another issue and tag it 4.1 e.g. as in 4.0 we aim at backwards compatibility then this is the way to go.

As for is_percent and moving validation there, I fully agree :+1: