docs: def get_value(cls, name):
          """ Returns the `value` of the `Category` member with the matching *name*
          or `None` if no member match.
  
          Example:
  
          >>> class Format(Category):
          ...     hour = 'hh'
          ...     minute = 'mm'
          ...     second = 'ss'
          >>> Format.get_value('hour')
          'hh'
          >>> Format.get_value('day')
  
          """
          for member in cls:
              if member.name == name:
                  return member.value
          return None