the tip of topic branches you are interested in from the output of
"git log next"). You should be able to safely build on top of them.
+However, at times "next" will be rebuilt from the tip of "master" to
+get rid of merge commits that will never be in "master. The commit
+that replaces "next" will usually have the identical tree, but it
+will have different ancestry from the tip of "master".
+
The "pu" (proposed updates) branch bundles the remainder of the
topic branches. The "pu" branch, and topic branches that are only in
"pu", are subject to rebasing in general. By the above definition