Re: [precis] Directionality rule (Was: Review of current document draft-ietf-precis-framework-20)

[Pete Resnick <[e-mail]>]

On 2/9/15 4:53 PM, Peter Saint-Andre - &yet wrote:
> On 2/9/15 1:42 PM, Pete Resnick wrote:
>
>> But give me a bit to chat with Klensin and we'll see if we can come 
>> up with sanity.
>
> I agree that the Bidi Rule from RFC 5893 is designed for use with DNS 
> labels, and that it's not a perfect fit for PRECIS strings. But it 
> might be the best we can do right now.

OK, here is some text that I worked on with John. We think this has the 
desirable properties that it is both as close to correct as we're going 
to get *and* what the WG intended. This is meant to be a replacement for 
all of the text in 5.2.5:

    The directionality rule of a profile specifies how to treat strings
    containing what are often called "right-to-left" (RTL) characters.
    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".  Using bidirectional
    strings in different layout contexts may yield display results that,
    while predictable to those who understand the display rules, may be
    counter-intuitive to casual users. Therefore some profiles may wish
    to restrict their use by specifying a directionality rule.

    The PRECIS framework does not directly address how to deal with
    bidirectional strings, since there is currently no widely accepted
    and implemented solution for the safe display of arbitrary
    bidirectional strings beyond the general Unicode bidirectional
    specification [UAX9]. Rules for management and display of
    bidirectional strings have been defined for domain name labels and
    similar identifiers in the "Bidi Rule" from [RFC5893]. If a profile
    really needs to specify a directionality rule, unless a great deal of
    careful research into the problems of displaying bidirectional text
    is done (which is outside of the scope of this framework), this
    document generally recommends using the  "Bidi Rule" from [RFC5893]
    for profiles based on IdentifierClass, and for profiles based on
    FreeformClass or other situations in which IdentifierClass is not
    appropriate, that consideration be given to using UAX #9 directly.

What do you think?

pr

-- 
Pete Resnick<http://www.qualcomm.com/~presnick/>
Qualcomm Technologies, Inc. - [phone]