No the xdg base directories spec. If you want to be able to opt in to dry on a system which doesn’t canonically use xdg vars, then you need some config.
XDG is cross-distribution for Linux, but it's not cross-platform. MacOS doesn't use XDG.
That’s my point. MacOS doesn’t use it, but many expect it to do so, so make this explicitly opt in so that a user’s preference is respected over the canonical configuration. To do that the best place to define the setting is in the spec.