vc-git short log format

[Chong Yidong]

vc-git sets log-view-message-re, for short logs, to

   "^\\(?:[*/\\| ]+ \\)?\\(?: ([^)]+)\\)?\\([0-9a-z]+\\)

Anyone know what the initial [*/\\| ] grouping is for?  I've only ever
seen git provide * at the start of each short log entry.  I've not seen
it print any of [/\\| ], or omit the asterisk entirely; when does that
happen?

(Asking because I'm working on toggling between short and long vc-log
entries, and it would be awfully convenient if I could just distinguish
expanded entries by indenting them.)