[PATCH] doc: be explicit about requests not returning a value

[Varad Gautam]

From: Varad Gautam <varad.gautam at collabora.com>

document how the asynchronous model works for requests and events to avoid
any confusion.

Signed-off-by: Varad Gautam <varad.gautam at collabora.com>
Suggested-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
---
 doc/publican/sources/Protocol.xml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/doc/publican/sources/Protocol.xml b/doc/publican/sources/Protocol.xml
index ba6b5f1..b8c30fe 100644
--- a/doc/publican/sources/Protocol.xml
+++ b/doc/publican/sources/Protocol.xml
@@ -52,7 +52,12 @@
       object ID and the event opcode, from which the client can determine
       the type of event.  Events are generated both in response to requests
       (in which case the request and the event constitutes a round trip) or
-      spontaneously when the server state changes.
+      spontaneously when the server state changes.  As the Wayland protocol
+      follows an asynchronous request model, there is no concept of
+      'return value' for requests.  A client can only receive information from
+      the server in the form of events.  Hence, if a client cannot proceed
+      without getting some information from the server, it must invoke a
+      round trip by issuing a <function>wl_display_roundtrip</function> call.
     </para>
     <para>
       <itemizedlist>
-- 
2.10.0