The "Xop" package provides Tcl/Tk with access to various low-level X window system functions. Its capabilities include:

   * The ability to query arbitrary windows on Tk's display
   * Access to and control of X cut buffers
   * Bell frequency, volume, and duration control
   * Access to X drawables, including dumping their contents to Tk images
   * Querying and manipulation of the X event queue
   * Reading of window-manager-related window properties
   * Colormap control

These facilities are provided via the "xop" tcl command. The intended purpose of the Xop package is to provide certain low-level X11 facilities required by window managers, but the package need not be used in that way.

http://www.eecs.umich.edu/~mckay/computer/xop0.3.tar.gz