I don't think I could do any better than the below. Thanks.
pr On 2/12/15 3:48 PM, Peter Saint-Andre - &yet wrote:
### 5.2.5. Directionality Rule The directionality rule of a profile specifies how to treat strings containing what are often called "right-to-left" (RTL) characters (see Unicode Standard Annex #9 [UAX9]). RTL characters come from scripts that are normally written from right to left and are considered by Unicode to, themselves, have right to left directionality. Strings containing RTL characters often also contain "left-to-right" (LTR) characters, such as numerals, as well as characters without directional properties. Consequently, such strings are known as "bidirectional strings". Presenting bidirectional strings in different layout systems (e.g., a user interface that is configured to handle primarily an RTL script vs. an interface that is configured to handle primarily an LTR script) can yield display results that, while predictable to those who understand the display rules, are counter-intuitive to casual users. In particular, the same bidirectional string (in PRECIS terms) might not be presented in the same way to users of those different layout systems, even though they are consistent within any particular layout system. In some applications, these presentation differences might be considered problematic and thus the application designers might wish to restrict the use of bidirectional strings by specifying a directionality rule. In other applications, these presentation differences might not be considered problematic (this especially tends to be true of more "free-form" strings) and thus no directionality rule is needed. The PRECIS framework does not directly address how to deal with bidirectional strings across all string classes and profiles, and does not define any new directionality rules, since at present there is no widely accepted and implemented solution for the safe display of arbitrary bidirectional strings beyond the Unicode bidirectional algorithm [UAX9]. Although rules for management and display of bidirectional strings have been defined for domain name labels and similar identifiers through the "Bidi Rule" specified in the IDNA2008 specification on right-to-left scripts [RFC5893], those rules are quite restrictive and are not necessarily applicable to all bidirectional strings. The authors of a PRECIS profile might believe that they need to define a new directionality rule of their own. Because of the complexity of the issues involved, such a belief is almost always misguided, even if the authors have done a great deal of careful research into the challenges of displaying bidirectional strings. This document strongly suggests that profile authors who are thinking about defining a new directionality rule think again, and instead consider using the "Bidi Rule" [RFC5893] (for profiles based on the IdentifierClass) or following the Unicode bidirectional algorithm [UAX9] directly (for profiles based on the FreeformClass or in situations where the IdentifierClass is not appropriate). ###
-- Pete Resnick<http://www.qualcomm.com/~presnick/> Qualcomm Technologies, Inc. - +1 (858)651-4478 _______________________________________________ precis mailing list [email protected] https://www.ietf.org/mailman/listinfo/precis
