From the old X.Org/X Consortium bug records - no patch was given though.
[An excellent starter project for someone wanting to get started working on
 X code.]

 Date: Wed, 12 Jul 1995 14:58:52 EST
 From: "Kaleb S. KEITHLEY" <kaleb@x.org>
 Subject: xmodmap: look up modifiers using the keysyms they're bound to.
 
 ### bug number:   7513
 ### area:         xmodmap
 ### severity:     enhancement
 ### priority:     low
 ### comments:     
 
 
 
      VERSION:
 
 R6, public-patch-12, all fix-trackers to date
 
      CLIENT MACHINE and OPERATING SYSTEM:
      DISPLAY TYPE:
      WINDOW MANAGER:
      COMPILER:
 
 N/A
 
      AREA:
 
 xmodmap
 
      SYNOPSIS:
 
 Look up modifiers using the keysyms they're bound to.
 
      DESCRIPTION:
 
 Enhance the language to look up modifiers by the keysym they are bound 
 to, e.g. if Mod1Mask is bound to Alt_L and Alt_R, allow references to 
 "Alt_L" or "Alt_R" to substitute for "mod1". Nominally this would only
 be useful for the 'clear' and possibly the 'remove' operation. As an
 example, given the following modifier map:
 
   #xmodmap -pm
   xmodmap:  up to 2 keys per modifier, (keycodes in parentheses):
 
   shift       Shift_L (0x1a),  Shift_R (0x61)
   lock        Caps_Lock (0x1c)
   control     Control_L (0x19),  Control_R (0x60)
   mod1        Alt_L (0x21),  Alt_R (0x41)
   mod2        Num_Lock (0x7e)
   mod3        Scroll_Lock (0x67)
   mod4      
   mod5      
 
 
 Something someone might want to do is clear all the keysyms from mod1,
 so they'd issue an 'xmodmap -e "clear mod1"'; Perhaps they would do this
 because they want to assign a different modifier to the Alt keys, and
 to do this they have to have explicit knowledge that the Alt keys are
 bound, in this case, to mod1. Ideally what they'd really like to do is
 is: 'xmodmap -e "clear Alt_L"' (or even just 'xmodmap -e "clear Alt"')
 or 'xmodmap -e "clear Num_Lock"' and have xmodmap do a lookup to find
 that Alt_L is bound to mod1 and then perform an equivalent 'xmodmap -e
 "clear mod1"'. In a 'xmodmap -e "remove Alt_R"' it would look up the
 modifier using "Alt_R" and then perform the equivalent 'xmodmap -e 
 "remove mod1 = Alt_R"'.
 
 In some respects this has some similarities to the way that 'xmodmap
 -e "keysym = ..."' looks up the keycode for the keysym and then does
 a keycode operation.
 
 Doing this would make xmodmap a little more flexible in that it doesn't
 require knowledge about the specific or current state of the modifier
 map. Then more generic .xmodmaprc scripts could be written that would
 work with any modifier map that a particular vendor might be shipping 
 or that any user might be using.
 
      REPEAT BY:
 
 N/A
 
      SAMPLE FIX:
 
 Maybe later.