[PATCH wayland] doc: Fill in high level description for Surfaces

[Bryce Harrington]

Signed-off-by: Bryce Harrington <bryce at osg.samsung.com>
---
 doc/publican/sources/Protocol.xml |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/doc/publican/sources/Protocol.xml b/doc/publican/sources/Protocol.xml
index b79b6be..2e48a7c 100644
--- a/doc/publican/sources/Protocol.xml
+++ b/doc/publican/sources/Protocol.xml
@@ -282,13 +282,23 @@
   <section id="sect-Protocol-Surface">
     <title>Surfaces</title>
     <para>
-      Surfaces are created by the client.
-      Clients don't know the global position of their surfaces, and
-      cannot access other clients surfaces.
+      A surface manages a rectangular grid of pixels that clients create
+      for displaying their content to the screen.  Clients don't know
+      the global position of their surfaces, and cannot access other
+      clients surfaces.
     </para>
     <para>
-      See <xref linkend="protocol-spec-interface-wl_surface"/> for the protocol
-      description.
+      A surface has a pair of content buffers that are swapped between
+      the client and the compositor.  Once the client has finished
+      writing pixels, it 'commits' the buffer; this permits the
+      compositor to access the buffer and read the pixels.  When the
+      compositor is finished with a buffer, it releases it back to the
+      client.  This way, the client can begin writing the next buffer
+      while the compositor is processing the current one.
+    </para>
+    <para>
+      See <xref linkend="protocol-spec-interface-wl_surface"/> for the
+      protocol description.
     </para>
   </section>
   <section id="sect-Protocol-Input">
-- 
1.7.9.5