[luatex] Hyphen character in tibetan

[Elie Roux]

Hello,

I'm typesetting tibetan and I'm facing a problem with hyphenation 
character : in tibetan, there is no space to separate words, instead 
there is a tsheg (་, U+F0B) between all syllables. There is no 
hyphenation character, but all lines are simply broken after any tsheg, 
and the remaining space at the end of the line is filled with other tshegs.

Right now I would only like to break the lines after a tsheg, but I 
cannot manage to do so with LuaTeX. Attached is an example with some 
attempts I made to do it (without any macro), which failed. I also 
attached the pdf with the result if I try to do it with a macro, because 
there are some strange black lines at the end of the lines.

Is there a way to break lines after a tsheg with LuaTeX without any 
macro? Why do these black lines appear? Could there be a way to fill the 
remaining space before the end of a line with other tshegs?

Also, are the non-zero width marks fixed in the ConTeXt code?

Thank you in advance,
-- 
Elie
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