docs/protocol-v2: clarify some ls-refs ref-prefix details

We've never documented the fact that a client can provide multiple
ref-prefix capabilities. Let's describe the behavior.

We also never discussed the "best effort" nature of the prefixes. The
client side of git.git has always treated them this way, filtering the
result with local patterns. And indeed any client must do this, because
the prefix patterns are not sufficient to express the usual refspecs
(and so for "foo" we ask for "refs/heads/foo", "refs/tags/foo", and so
on).

So this may be considered a change in the spec with respect to client
expectations / requirements, but it's mostly codifying existing
behavior.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

Documentation/technical/protocol-v2.txt

@@ -193,7 +193,11 @@ ls-refs takes in the following arguments:
 	Show peeled tags.
     ref-prefix <prefix>
 	When specified, only references having a prefix matching one of
-	the provided prefixes are displayed.
+	the provided prefixes are displayed. Multiple instances may be
+	given, in which case references matching any prefix will be
+	shown. Note that this is purely for optimization; a server MAY
+	show refs not matching the prefix if it chooses, and clients
+	should filter the result themselves.
 
 If the 'unborn' feature is advertised the following argument can be
 included in the client's request.