git/Documentation/config/lsrefs.txt

lsrefs.unborn::
	May be "advertise" (the default), "allow", or "ignore". If "advertise",
	the server will respond to the client sending "unborn" (as described in
	protocol-v2.txt) and will advertise support for this feature during the
	protocol v2 capability advertisement. "allow" is the same as
	"advertise" except that the server will not advertise support for this
	feature; this is useful for load-balanced servers that cannot be
	updated atomically (for example), since the administrator could
	configure "allow", then after a delay, configure "advertise".