[XeTeX] (not) understanding XeTeXinterchartoks

[Adam Twardoch (List)]

In modern text processing (Unicode+OpenType), a text run is a series of characters with the same formatting (font, size, color etc.), directionality (ltr, rtl) and script (writing system such as Latin, Greek, Arabic or Gujarati).

A. 

Sent from my mobile phone.

> On 08.05.2015, at 11:45, David Carlisle <d.p.carlisle at gmail.com> wrote:
> 
> 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
> 
> 
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