Documentation/config/lsrefs.txt

   1 lsrefs.unborn::
   2         May be "advertise" (the default), "allow", or "ignore". If "advertise",
   3         the server will respond to the client sending "unborn" (as described in
   4         linkgit:gitprotocol-v2[5]) and will advertise support for this feature during the
   5         protocol v2 capability advertisement. "allow" is the same as
   6         "advertise" except that the server will not advertise support for this
   7         feature; this is useful for load-balanced servers that cannot be
   8         updated atomically (for example), since the administrator could
   9         configure "allow", then after a delay, configure "advertise".