docs: def between(min_value, max_value):
      'Numerical values limit'
      message = N_('value should be between %(min)d and %(max)d') % \
                      dict(min=min_value, max=max_value)
  
      @validator(message)
      def wrapper(conv, value):
          if value is None:
              # it meens that this value is not required
              return True
          if value < min_value:
              return False
          if value > max_value:
              return False
          return True
      return wrapper