+*set-default* [<subvolume>|<id> <path>]::
+Set the default subvolume for the (mounted) filesystem.
+
+Set the default subvolume for the (mounted) filesystem at <path>. This will hide
+the top-level subvolume (ie. the one mounted with 'subvol=/' or 'subvolid=5').
+Takes action on next mount.