...
dists/stable/non-free/source/
-dists/testing
-[everything like in stable]
+dists/testing/
+dists/testing/main/
+ ...
+dists/testing/contrib/
+ ...
+dists/testing/non-free/
+ ...
dists/unstable
-[ditto]
+dists/unstable/main/
+ ...
+dists/unstable/contrib/
+ ...
+dists/unstable/non-free/
+ ...
pool/
pool/a/