[luatex] How to get a \mid binary relation that grows in LuaTeX

[Ulrike Fischer]

Am Wed, 15 Nov 2017 22:13:25 +0100 schrieb Hans Hagen:

> the next version will use the normal class numbers

Can one query the number by name? So that 
\Umiddle class \directlua{whatever(rel)}  gives now 5 and in the
next version 3?


-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/