You should use ARABIC SHADDA U+0651 in all positions. The presentation forms (isolated, medial, final forms) are for compatibility with legacy systems. See what is said in http://www.unicode.org/versions/Unicode7.0.0/ch09.pdf about the Arabic Presentation Forms-B.
Cheers, On Fri, 15 May 2015 at 15:53 عبد الرحمان أيمن <abdo.alrhman.ai...@gmail.com> wrote: > hi, > > regarding the Arabic diacritics. e.g. for the Shadda, we > have: > > 1. The form that people type: > http://unicode-table.com/en/0651/ > > 2. An Isolated form. It should be the same, but looks different in the > Unicode table, which is confusing me now. > http://unicode-table.com/en/FE7C/ > > 3. A medial form: > http://unicode-table.com/en/FE7D/ > > When do I use 1/2, and when do I use 3? > > some diacritics has e.g. isolated and medial forms. Some have > only one of these forms, some have both. So, where does each of them go? > > respectfully > >