[Nut-upsuser] What does ENUM mean?

[Roger Price]

I am trying to understand the specification of subcommand ENUM in
https://networkupstools.org/docs/developer-guide.chunked/ar01s09.html

This says:

  ENUM
  Form:
    LIST ENUM <upsname> <varname>
    LIST ENUM su700 input.transfer.low

  Response:
    BEGIN LIST ENUM <upsname> <varname>
    ENUM <upsname> <varname> "<value>"
    ...
    END LIST ENUM <upsname> <varname>

    BEGIN LIST ENUM su700 input.transfer.low
    ENUM su700 input.transfer.low "103"
    ENUM su700 input.transfer.low "100"
    ...
    END LIST ENUM su700 input.transfer.low

What exactly does command LIST ENUM call for?  Is it a list of those variables 
for which there is a fixed set of possible values?

Roger