We need ability to force change window icon to user icon through dialog "System settings" -> "Window behavior" -> "Window rules". Reproducible: Always Steps to Reproduce: 1. Open idle (python ide, gui used Tcl/tc). 2. Press alt+tab. Actual Results: "idle" window has default X icon. Rules in "System settings" -> "Window behavior" -> "Window rules" does not allow to change window icon. Expected Results: Icon of "idle" window must be python logo. We use rules in "System settings" -> "Window behavior" -> "Window rules" for change window icon. Another example. "gimp" uses small copy of edited image as window icon. We must can prevent these behavior and set constant icon with window rules. Yet another example. "Flash player" (full screen) does not have application icon and does not have normal window class name (just "exe"). We must have way to change "Flash player's" window properties (include icon).
The correct way here is to fix the client to set an icon. -> file a bugreport there. This approach is totally gonna fail if the client wants to set icons to indicate certain states or whatever. The rules are meant to workaournd client bugs, not to fix a whole category of clients (python, wine, whatever) The present way to alter the icon is to just set the resp. X11 property. Undetectable windows (casually "wine") could not be handled through this at all - you could only assign an icon at runtime (what is certainly not what you want)