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 -------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex