x11test.c

KeySym sym = XKeycodeToKeysym(display, event.xkey.keycode, event.xkey.state & ShiftMask ? 1 : 0);

XGrabKey(dpy, XKeysymToKeycode(dpy, XK_F1), Mod1Mask, DefaultRootWindow(dpy), True, GrabModeAsync, GrabModeAsync);
XGrabKey(dpy, XKeysymToKeycode(dpy, XK_F2), Mod1Mask, DefaultRootWindow(dpy), True, GrabModeAsync, GrabModeAsync);

// XK_Tab
// XK_Escape

// move this window back to its original size at 0, 0.
if (ev.type == KeyPress && ev.xkey.keysym == XK_Tab)
{
  XMoveResizeWindow(dpy, start.subwindow, 0, 0, attr.width, attr.height);
}