+USAGE='[--onto <newbase>] <upstream> [<branch>]'
+LONG_USAGE='If <branch> is specified, switch to that branch first. Then,
+extract commits in the current branch that are not in <upstream>,
+and reconstruct the current on top of <upstream>, discarding the original
+development history. If --onto <newbase> is specified, the history is
+reconstructed on top of <newbase>, instead of <upstream>. For example,
+while on "topic" branch: