[PATCH wayland] protocol: add a note about the version bumps on wl_seat

[Peter Hutterer]

See the explanation by Jonas here:
http://lists.freedesktop.org/archives/wayland-devel/2015-March/020814.html

---
One thought while writing this: would it make sense to add a
wl_seat.get_pointer_versioned request to request a specific wl_pointer
version from the seat? or is that a solution waiting for a problem?

 protocol/wayland.xml | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index 880f90a..22606bb 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -1329,6 +1329,14 @@
     </request>
    </interface>
 
+  <!-- Note regarding the wl_seat version:
+       The wl_pointer, wl_touch, wl_keyboard must be identical to the
+       wl_seat version. Bumping one requires bumping all of them.
+
+       Reason: clients cannot specify a version in wl_seat.get_pointer,
+       wl_seat.get_keyboard or wl_seat.get_touch, the returned object is
+       always of the same version as the wl_seat.
+   -->
   <interface name="wl_seat" version="4">
     <description summary="group of input devices">
       A seat is a group of keyboards, pointer and touch devices. This
@@ -1402,6 +1410,7 @@
 
   </interface>
 
+  <!-- for the version see the comment in wl_seat -->
   <interface name="wl_pointer" version="4">
     <description summary="pointer input device">
       The wl_pointer interface represents one or more input devices,
@@ -1611,6 +1620,7 @@
 
   </interface>
 
+  <!-- for the version see the comment in wl_seat -->
   <interface name="wl_keyboard" version="4">
     <description summary="keyboard input device">
       The wl_keyboard interface represents one or more keyboards
@@ -1725,6 +1735,7 @@
     </event>
   </interface>
 
+  <!-- for the version see the comment in wl_seat -->
   <interface name="wl_touch" version="3">
     <description summary="touchscreen input device">
       The wl_touch interface represents a touchscreen
-- 
2.3.3