[no subject]

   Whenever this spec speaks about "sending a message to the root
   window", it is understood that the client is supposed to create a
   ClientMessage event with the specified contents and send it by using a
   SendEvent request with the following arguments:

      destination     root
      propagate       False
      event-mask      (SubstructureNotify|SubstructureRedirect)
      event           the specified ClientMessage

I suggest to add the following (in a better English):

  The  xclient.window member of the event structure should be set to the
  Root window id (or None) if the message concerns a root property or
  to the window id of the concerned window for a window property.
  Moreover, the xany.window member should be set to the window id of the
  main window of the application which sends the message. Rational: this
  allows the window manager to know which application send the client
  message.

I find this useful to be able to configure the wm to reject some client
messages that the user does not want. Example: One may want to reject
some messages that ask to switch a window to an other desktop
if it is the application window  owner which asks this and accept
the message if it is not the case (and it it is probably a taskbar
which send the message).

Regards, Olivier