Documentation/config/fmt-merge-msg.txt

   1 merge.branchdesc::
   2         In addition to branch names, populate the log message with
   3         the branch description text associated with them.  Defaults
   4         to false.
   5
   6 merge.log::
   7         In addition to branch names, populate the log message with at
   8         most the specified number of one-line descriptions from the
   9         actual commits that are being merged.  Defaults to false, and
  10         true is a synonym for 20.