Friday, September 2, 2011

PRI #205: Proposed addition of AL MARK and LEVEL DIRECTION MARK

The Unicode Technical Committee has posted a new issue for public review and comment. Details are on the following web page:
Review period for the new item closes October 24, 2011. Please see the page for links to discussion and relevant documents. Briefly, the new issue is:

PRI #205 Proposed addition of AL MARK and LEVEL DIRECTION MARK

The UTC is considering proposals for two characters to help address various difficult issues in bidirectional text layout. These two characters are similar to the already-encoded LRM and RLM.

1. The proposed AL MARK (ALM) provides a direction mark with Bidi_Class AL in order to complete the set of direction marks with strong direction classes (L, R, AL). It requires no additional Bidi_Class value or change to the Unicode Bidirectional Algorithm (UBA).

2. The proposed LEVEL DIRECTION MARK (LDM) behaves like a direction mark which dynamically takes on the resolved direction associated with the current embedding level. While the optimum implementation would use a new Bidi_Class value, this is prohibited by the Unicode Character Encoding Stability Policy. Several alternatives are described. Note: In earlier discussions the LDM was referred to as EMBEDDING LEVEL MARK (ELM).

Please see the background document for details, including alternative implementation options.