I am in the process of setting up a local mirror of the Raspbian repository. I have successfully mirrored the archive.raspbian.org repo using rsync, however I noticed in the sources.list.d directory there is the following line
deb http://archive.raspberrypi.org/debian/ stretch main ui
What packages are stored here? Also what is the idea of splitting between the two sources? I can't seem to find any information describing the difference.