231	Bidi Parenthesis Algorithm	2012.07.23
Status:	Closed
Originator:	UTC
Informal Discussion:	Unicode Mail List (Join)
Formal Feedback:	Contact Form
Resolution:	A proposed update of UAX #9 will be issued for Unicode version 6.2.1, including a version of the BPA proposal discussed in the August 2012 UTC meeting.

Description of Issue:

The Unicode Technical Committee is seeking feedback on a proposal to enhance the Unicode Bidirectional Algorithm (UAX #9) with additional logic—a bidirectional parenthesis algorithm (BPA)—for processing paired punctuation marks such as parentheses. This proposal is intended to produce better bidi-layout results in common text sequences that involve paired punctuation marks.

The proposal document considers two approaches that could be taken to incorporate the enhancement into UAX #9:

• Incorporate the BPA directly into the core UBA algorithm in the form of a new rule, N0.
• Document the BPA in UAX #9 as a supplemental higher-level protocol that can optionally be used in implementations.

See the Background Document.

The following are some specific points on which feedback is requested (section numbers refer to sections in the background document):

• Is a solution to the current problem of mismatched parenthesis desirable? (§§ 1 and 2)
• Does the proposed solution meet expectations in terms of the naturalness of segmentation and directional flow of enclosed units? (§§ 3 and 5)
• Should the BPA be implemented as a new rule affecting the resolution of neutral types in the core UBA – proposed rule N0? (§ 4.1)
• Should the BPA, rather, be a recommended implementation using higher level protocols? (§ 4.2)
• Are stability concerns adequately addressed? (§ 6)
• Are interoperability concerns during the migration period adequately addressed? (§ 6)

Feedback on any other aspect of the proposal is, of course, also welcomed.

The Unicode Technical Committee has also received an independent, but related, proposal to encode additional bidi control characters. These would allow adjacent runs of text to be isolated from one another in terms of bidi-layout effects. That proposal follows recent W3C enhancements to HTML and CSS, which add corresponding bidi-layout control mechanisms (the unicode-bidi:isolate and unicode-bidi:plaintext properties). The problem scenarios of concern for the BPA proposal overlap at least in part with those of this other initiative.

For information about how to discuss this issue and how to supply formal feedback, please see the feedback and discussion instructions. The accumulated feedback received so far on this issue is shown below, or you can look at a full page view.