git/Documentation/config/fmt-merge-msg.txt

merge.branchdesc::
	In addition to branch names, populate the log message with
	the branch description text associated with them.  Defaults
	to false.

merge.log::
	In addition to branch names, populate the log message with at
	most the specified number of one-line descriptions from the
	actual commits that are being merged.  Defaults to false, and
	true is a synonym for 20.

merge.suppressDest::
	By adding a glob that matches the names of integration
	branches to this multi-valued configuration variable, the
	default merge message computed for merges into these
	integration branches will omit "into <branch name>" from
	its title.
+
An element with an empty value can be used to clear the list
of globs accumulated from previous configuration entries.
When there is no `merge.suppressDest` variable defined, the
default value of `master` is used for backward compatibility.