Not really. Even if there is only one typeface involved, the joining behavior of Arabic letters is normative and in scope.
This means that even if there's a font change between two letters (for example due to a fallback for some letters or diacritics), each letter should contonue to adopt its normative joining behavior (i.e. displaying their correct joining form). Then the renderer will just make a "best effort" to place the diacritics on them (even if those diacritics comes from another font than the base letter), but of course the ligatures of letters will not be generated, and it's possible that two letters that are normally joining perfectly will not join completely their joining strokes, even if each letter is shown in their correct form. If one wanted to disable the normative joining forms of letters, as ZWNJ can be used between them. I also think that the renderer should also be able to use base letters and diacritics found in a font by decomposing advanced characters that are encoded in the UCS with a single code point, if ever that character is not mapped in the font, using a best effort to place the diacritics, instead of trying to fond a fallback font that would map the composite character. Le 30 mars 2012 20:08, Julian Bradfield <jcb+unic...@inf.ed.ac.uk> a écrit : > On 2012-03-30, Andreas Prilop <prilop4...@trashmail.net> wrote: >> I think a better idea is to have joining glyphs always even for >> different typefaces. At least the Unicode Standard should say >> what should happen when Arabic characters of different typefaces >> follow each other. > > How can it? Unicode is about plain text. As soon as you start talking > about different typefaces, you're out of scope.