On Mon, 01 May 2017 12:05:06 +0200
Ulrich Mueller <ulm@gentoo.org> wrote:

> Please make this DEFAULT_VALUE, in oder to be consistent with the
> existing DEFAULT_UNSET. Otherwise, nobody will be able to remember
> when to use a hyphen and when an underscore. 

Initial version did use _, but mgorny seems to be pushing for the
change to happen in the
other direction.

So this is just "-" until we decide for sure what's happening there and
I'll follow whatever standard we decide upon.