+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:
+
+ A---B---C topic
+ /
+ D---E---F---G master
+
+ $ '"$0"' --onto master~1 master topic
+
+would rewrite the history to look like this:
+
+
+ A'\''--B'\''--C'\'' topic
+ /
+ D---E---F---G master
+'
+