Unicode has many "control characters" that only control text behaviour
and shouldn't be rendered visually in the text, such as Bidi_Control and
Join_Control chars (see
http://www.unicode.org/Public/5.1.0/ucd/PropList.txt and
http://unicode.org/Public/UNIDATA/UCD.html)

Currently, ConTeXt handles ZWJ and ZWNJ, but other characters get
rendered if the font has glyphs for them or make no effect at all if the
font has no glyphs for them. I think that the optimum behaviour is to
make those characters affect text formatting while not visually rendered
whether the font has glyphs for them or not.
It might be also useful if we can enable rendering those characters
manually, for drafts and such.

Regards,
 Khaled


-- 
 Khaled Hosny
 Arabic localizer and member of Arabeyes.org team