[luatex] Missing math primitive & assorted remarks

[ulrik.vieth at arcor.de]

> I don't know if this is necessarily behaviour that you'd like to replicate
> (you could also imagine using the legacy output for regular old mathchars
> and using the extended output for larger values). Like I said, I'm not aware
> of any direct problems this might cause; I simply wanted to let you know
> just in case.
 
Sorry for jumping into this discussion, but there was another thing 
I noticed recently while testing LuaTeX vs. XeTeX.

In LuaTeX the \tracingall ouput (e.g. for assembling boxes) shows 
Unicode characters. These are sometimes not printable on some terminals 
(depending on screen fonts) and it may be difficult to determine exactly
which glyphs are used.

In XeTeX the \tracingall output shows something like glyph#3456,
but those numbers are not the Unicode characters, but seem to be
a technical index in the font file.

I wonder what would be the best way of showing which glyphs are used,
especially in the presence of substitions (e.g. prime -> prime.ssty).
You could display prime as U+2032 or ^^^^2032, but how would 
you display prime.ssty.  Would it be something like U+F0xxxx?

Just an idea.

Regards, Ulrik