Re: WONTFIX in KDE
I call BS on this as well.
X11 has the concept of window hierarchy. Starting at the root window, which IIRC always has window ID 0, is is possible to traverse the complete hierarchy, obtaining the window ID, the name of the application and it's window name, it's colour depth, position and hints.
Find the xprop and xwininfo binaries, run them, and point each at a window. Everything that is printed has been obtained through the X11 properties of the window. kwin is acting as an X11 window manager, so automatically has access to all this information.
I don't know how this will be altered in Wayland or Mir, but X11 (either in it's MIT, XFree86 or X.org guise) has been the standard windowing framework on Linux and UNIX (the exceptions being very old Sun and Apollo systems [if you remember them - although not strictly UNIX], and Mac OSX) for a very long time.