[XeTeX] (not) understanding XeTeXinterchartoks

[David Carlisle]

The following plain xetex document loops forever on \show\tmpb
the \show don't cause the looping, if they are replaced by
\def\zzzb{} xetex just hangs in a tight loop.

The fact that it loops isn't necessarily a bug.
 \def\zzz{\zzz}\zzz
does the same,  but are there any words that could be added to
the manual so that I could have predicted this?

I'm not sure why 255 is being triggered at all as
the X is being inserted into the middle of an existing hlist.

The manual says 255 represents

> a boundary between a `run' of characters and something else

So I guess I am asking what 'run' means in this context:-)



David



\XeTeXinterchartokenstate = 1

\newXeTeXintercharclass \Xclass
\XeTeXcharclass `\X \Xclass

\XeTeXinterchartoks 0 \Xclass = {\zza}
\XeTeXinterchartoks 255 \Xclass = {\zzb}


\def\zza{\futurelet\tmpa\zzza}
\def\zzza{\show\tmpa}

\def\zzb{\futurelet\tmpb\zzzb}
\def\zzzb{\show\tmpb}



xxxXxxx


\bye