#87 was nonsense, as I commented in that issue.

Relative XDG_CACHE_HOME just doesn't make any sense, relative to what.

https://www.freedesktop.org/wiki/Specifications/basedir-spec/ links to latest, which says

All paths set in these environment variables must be absolute. If an implementation encounters a relative path in any of these variables it should consider the path invalid and ignore it.

There's even the source: https://github.com/freedesktop/xdg-specs/tree/master/basedir with history, https://github.com/freedesktop/xdg-specs/commits/master/basedir/basedir-spec.xml