Comment 1 for bug 1474417

attaching a diff from squid-deb-proxy.conf [1] to debian/extras/maas-proxy.conf [2]

[1] http://bazaar.launchpad.net/~squid-deb-proxy-developers/squid-deb-proxy/trunk/view/head:/squid-deb-proxy.conf
[2] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/wily/maas/wily/view/head:/debian/extras/maas-proxy.conf

$ mydiff() { myd=$(mktemp -d); for f in "$1" "$2"; do grep -v "^#" "$f" | sort -u > "$myd/${f##*/}"; done; diff -u "${myd}/${1##*/}" "${myd}/${2##*/}"; rm -Rf "$myd"; }
$ mydiff squid-deb-proxy.conf debian/extras/maas-proxy.conf

Pay particular difference to refresh_pattern:
-refresh_pattern changelogs.ubuntu.com\/.* 0 1% 1
-refresh_pattern deb$ 129600 100% 129600
-refresh_pattern \/InRelease$ 0 0% 0 refresh-ims
-refresh_pattern \/(Packages|Sources)(|\.bz2|\.gz|\.xz)$ 0 0% 0 refresh-ims
-refresh_pattern \/Release(|\.gpg)$ 0 0% 0 refresh-ims
-refresh_pattern tar.bz2$ 129600 100% 129600
-refresh_pattern tar.gz$ 129600 100% 129600
-refresh_pattern tar.xz$ 129600 100% 129600
-refresh_pattern \/(Translation-.*)(|\.bz2|\.gz|\.xz)$ 0 0% 0 refresh-ims
-refresh_pattern udeb$ 129600 100% 129600
+refresh_pattern . 0 20% 4320
+refresh_pattern ^ftp: 1440 20% 10080
+refresh_pattern -i (/cgi-bin/|\?) 0 0% 0
+refresh_pattern (Release|Packages(.gz)*)$ 0 20% 2880

The new change for squid-deb-proxy.conf is the addition of the Translation line.
Note other differences:
 * maas-proxy does not pay special attention to .bz2 or .xz files (only .gz)
 * maas-proxy does not pay special attention to .gpg files
 * squid-deb-proxy uses 'refresh-ims' while maas's version does not.

http://www.squid-cache.org/Doc/config/refresh_pattern/ has info on what those lines are (refresh_pattern regex min max [options])