+# <upstreaminfo> is
+# [,][<subdir>:][+]<commitid>[,...]
+#
+# if initial comma is supplied, entries are not positional. Unspecified
+# <subdir> means root (and there may be only one).
+# xxx want auto branch names
+# xxx too complicated
+# how about for now
+# [+]<commit> [<subdir:> [+]<commit>...]
+# ? plus options
+# --new-upstream-different-subtrees
+
+# UPSTREAM[,[[SUBDIR:]SUBUPSTREAM]
+# default for SUBDIR: is from previous upstream merge[xxx terminology]
+#
+#