def is_os(string)
      return false if string === false || string === true || string.nil?
      @os.key?(string.to_sym)
    end
def is_os(string)
      return false if string === false || string === true || string.nil?
      @os.key?(string.to_sym)
    end
Returns `true` if provided value is a registered OS
 @param string [String, Symbol] value to check
 @return [TrueClass, FalseClass]