[PATCH] docs: Add a note about unmapping surfaces without content

[matthias.clasen at gmail.com]

From: Matthias Clasen <mclasen at redhat.com>

Explanation received on wayland-devel indicates that it is
expected compositor behaviour to unmap surfaces without content.
---
 protocol/wayland.xml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index 718a4a5..548b1b9 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -923,6 +923,9 @@
 
 	Only if wl_surface.attach is sent with a NULL wl_buffer, the
 	following wl_surface.commit will remove the surface content.
+        It is up to the compositor implementation how it will treat
+        a surface without content; a common behaviour is to unmap
+        the surface until it gets defined content again.
       </description>
 
       <arg name="buffer" type="object" interface="wl_buffer" allow-null="true"/>
-- 
1.8.2