Khaled notes: "There are so many issues with MS implementation(s), for example you can not combine any arbitrary Arabic diacritical marks on any given base character. I don't think Unicode need to invent workaround broken vendor implementations, interested parties should instead pressure on that vendor to fix its implementation(s)."
The MS Office math facility allows combining marks in the range U+0300..U+036F and most in the range U+20D0..U+20F0 to be applied to any base character(s) including complicated mathematical expressions. Such generality is needed in mathematics, since tildes, hats, bars, etc., are displayed over multiple base characters such as the expression a+b. Hebrew and Arabic combining marks aren't currently treated as valid mathematical combining marks, so the sequence U+25CC U+05BC U+05B8 doesn't render as Vincent desires in a math zone. It seems reasonable to allow all Unicode combining marks as accents in math zones. Murray
