I think the zero-width joiner (ZWJ, U+200D) should join
regardless of typeface. But Internet Explorer 8 won't join
if the ZWJ is taken from another font than surrounding text.
In MS Windows, the font Mangal contains the zero-width joiner
but not Arabic letters. When I specify "font-family: Mangal"
then Internet Explorer 8 takes the ZWJ from Mangal but
Arabic letters from another font and the result is non-joining.
See the attached file zwj.html.
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