code: def validate_arg(arg, parent, key, arg_type)
        result = case arg
          when Array
            validate_array_arg(arg, parent, key, arg_type)
          when Hash
            validate_hash_arg(arg, parent, key, arg_type)
          when Time
            arg = validate_time_arg(arg, parent, key)
            validate_hash_arg(arg, parent, key, arg_type)
          else
            arg
        end
        return result
      end
docs: Validates single argument.