code: def __ipv6_netmask(value):
      '''validate an IPv6 integer netmask'''
      valid, errmsg = False, 'IPv6 netmask (0->128)'
      valid, value, _ = __int(value)
      valid = (valid and 0 <= value <= 128)
      return (valid, value, errmsgf __ipv6_netmask(value):
      '''validate an IPv6 integer netmask'''
      valid, errmsg = False, 'IPv6 netmask (0->128)'
      valid, value, _ = __int(value)
      valid = (valid and 0 <= value <= 128)
      return (valid, value, errmsg)
docs: validate an IPv6 integer netmask