docs: def host(value):
      """ Validates that the value is a valid network location """
      if not value:
          return (True, "")
      try:
          host,port = value.split(":")
      except ValueError as _:
          return (False, "value needs to be <host>:<port>")
  
      try:
          int(port)
      except ValueError as _:
          return (False, "port component of the host address needs to be a number")
  
      return (True, "")