While experimenting with tc-functions I encountered something that seems like a bug. The function autoscan-devices returns: sda1 sr0 tcvd on my system. I use tcvd, and my extension directory is tcvd/tce3. The autoscan function iterates through this list of three devices, and "find_mountpoint sr0" actually returns "/mnt/tcvd" (I don't have a CD in the drive). It seems as though it should return an empty string because no disc is mounted, and I suspect it does if tcvd is not used.
This is a problem because $(autoscan tce3 d) returns sr0 instead of tcvd, which means that autoscanning for a directory within tcvd does not work. This doesn't affect me, but I thought I'd mention it anyway.