Oftenly, a torrent consists of lots of files but you just want to download only few of them. This feature is requested by many users especially low-bandwidth users who don't want to waste their bandwidth. According to BitTornado, it has supported this feature since last version. In BTQueue, it is enabled for easier use since 0.0.18.
Actually, file selector in BTQueue is just to assign priority to each files in a torrent. There are 4 possible priorities from -1 until 2. -1 means to disable downloading this file. 0 is the highest priority while 2 is the lowest priority. In conclusion, BTQueue does not download files with priority -1 and it will download files with priority 0 prior to priority 2.
There are 2 scenarios to specify priorities to each torrent. For newly added torrent, you can specify its priority directly as an option to add command. For example, a torrent consists of 2 files.
add -p -1,0 http://abc.com/abc.torrent
In other case, a torrent has been added and you want to specify its priorities. At this point, lset
command can be used.
lset 1 priorities -1,0