The following sample would crash luatex using context distriputed luatex-plain format: %%% \font\arab="SimpleNaskhi.ttf:script=arab;language=dflt;mode=node;+init;+medi;+fina;+rlig;+liga;+mark"\arab \textdir TRT اللهِ \bye %%% (the font used http://code.google.com/p/raqm/source/browse/trunk/fonts/simplenaskhi/SimpleN...) With the message: %%% error: ...texmf/tex/plain/luatex-plain/luatex-fonts-merged.lua:7765: attempt to call field 'register_message' (a nil value) %%% It seems that fonts.register_message is not defined. Pressing enter after that will crash luatex: %%% luatex: ../../../source/texk/web2c/luatexdir/tex/linebreak.c:1660: ext_do_line_break: Assertion `varmem[((cur_p)+1)].hh.v.RH == 0+4+4+4+4+4+4+2+2+2' failed. Aborted %%% Regards, Khaled -- Khaled Hosny Arabic localiser and member of Arabeyes.org team Free font developer