Re: Interrobang

    pdfjadetx, not pdftex.  I've no idea if there's any relationship between 
    those two apps.

(pdf)jadetex and (pdf)xmltex are TeX formats (large set of TeX macros)
that run on top of pdftex (the actual compiled binary).
https://tug.org/levels.html

      (So this whole discussion is in the wrong place--sorry, 

Not to worry, this is as good a place as any, since there is no
dedicated place for {jade,xml}tex discussion. Especially since DavidC
(probably the last principal author left standing) is here :). (And, I
am surprised and glad to know that anyone is still using them.) --best, karl.