Question on X modifier key handling

[Fred Kiefer]

Last night when chasing another problem, valgrind memcheck reported a 
problem in check_modifiers() in XGServerEvent.m. I think the reported 
problem is non-existent, but it got me thinking about this code.

// checks whether a GNUstep modifier (key_sym) is pressed when we're 
only able
// to check whether X keycodes are pressed in xEvent->xkeymap;
static int check_modifier (XEvent *xEvent, KeySym key_sym,
                           XModifierKeymap *modmap)
{
    char *key_vector;
    int by,bi;

    // implementation fails if key_sym is only accessible by a multi-key
    // combination, however this is not expected for GNUstep modifier keys;
    // to fix implementation, would need to first determine modifier 
state by
    // a first-pass scann of the full key vector, then use the state in 
place
    // of "0" below in XKeycodeToKeysym
    key_vector = xEvent->xkeymap.key_vector;
    for (by=0; by<32; by++) {
        for (bi=0; bi<8; bi++) {
            if ((key_vector[by] & (1 << bi)) &&

(XKeycodeToKeysym(xEvent->xkeymap.display,by*8+bi,0)==key_sym))
                return 1;
        }
    }
    return 0;
}

Why don't we just convert the handed in key_sym into a keycode with 
XKeysymToKeycode and check the map just for that single key?
But then I am not sure what this function is used for at all. It gets 
called when a KeymapNotify event happens. There we still get a modifier 
map, which we no longer use anywhere.
This whole event is normally send just after a FocusIn and EnterNotify 
event and the later at least already has the modifiers in the status 
field. Wouldn't it be better to register all the special GNUstep 
modifier keys as X modifiers and rely on X to handle them correctly. But 
as said, I really don't understand this area.