I don't think it 'goes against' anything... it's simply a more concise way of doing the .include? - it's syntactic sugar. And as he points out, 'in' is already

I don't think it 'goes against' anything... it's simply a more concise way of doing the .include? - it's syntactic sugar. And as he points out, 'in' is already a keyword anyway - so if it makes a more readable way of doing things, then why not?