Another complication. On Windows, this line doesn't do what it claims:

if (event.state & 12) != 0 and event.keysym == "Home":
    # state&1==shift, state&4==control, state&8==alt
    return # <Modifier-Home>; fall back to class binding

The comment says state&8==alt, but this is wrong. state&8==mod1, and on
Windows Tk defines mod1 to be num-lock. So if you have num-lock on,
home_callback will always fall back to the standard binding.

See the Tk source:
xlib/X11/X.h   defines Mod1Mask
win/tkWinX.c   maps VK_NUMLOCK to Mod1Mask