Unicode Arabic Mark Rendering UTR #53 Now Published

The combining classes of Arabic combining characters in Unicode are different than combining classes in most other scripts. They are a mixture of special classes for specific marks plus two more generalized classes for all the other marks. This has resulted in inconsistent and/or incorrect rendering for sequences with multiple combining marks since Unicode 2.0.

The Arabic Mark Transient Reordering Algorithm (AMTRA) described in UTR #53 is the recommended solution to achieving correct and consistent rendering of Arabic combining mark sequences. This algorithm provides results that match user expectations and assures that canonically equivalent sequences are rendered identically, independent of the order of the combining marks.

The concepts in this algorithm were first proposed four years ago by Roozbeh Pournader. We are pleased it has now been published as an official Technical Report.

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Proposed Draft UTR #53, Unicode Arabic Mark Ordering Algorithm Now Available for Public Review

The Unicode Consortium has released Proposed Draft Unicode Technical Report #53, Unicode Arabic Mark Ordering Algorithm. This UTR describes an algorithm for determining correct rendering of Arabic combining mark sequences.

The combining classes of Arabic combining characters in Unicode are a mixture of special classes for specific marks plus two more generalized classes for all the other marks. For many years this has resulted in inconsistent rendering for sequences with multiple combining marks such as:

The algorithm described in this UTR provides a method to reorder Arabic combining marks in order to accomplish the following goals:

• The inside-out rendering rule will display combining marks in the expected visual order.
• Ensure identical display of canonically equivalent sequences.
• Provide a mechanism for overriding the display order in exceptional cases.

The document is in “Proposed Draft” state, and made available for public review and comment. Information about this type of document can be found on the About Unicode Technical Reports page.

For information about how to discuss this Public Review Issue and how to supply formal feedback, please see the PRI #359 page.