On 2/9/15 11:16 AM, Peter Saint-Andre - &yet wrote:
On 2/9/15 10:20 AM, Pete Resnick wrote:
Crap. Somehow I missed this discussion back in December, and didn't
notice it before I sent out Last Call. When I went to put in my new
ballot, I saw the change.
On 12/7/14 9:49 PM, Peter Saint-Andre - &yet wrote:
5.2.5. Directionality Rule
The directionality rule of a profile specifies how to treat
strings containing left-to-right (LTR) and right-to-left (RTL)
characters (see Unicode Standard Annex #9 [ UAX9 ]). A profile
usually specifies a directionality rule that restricts strings to
be entirely LTR
strings or entirely RTL strings and defines the allowable
sequences of characters in LTR and RTL strings. Possible rules
include, but are not limited to, (a) considering any string that
contains a right- to-left code point to be a right-to-left string,
or (b) applying the "Bidi Rule" from [ RFC5893 ].
One can not restrict to only LTR or RTL as some code points are
neutral regarding directionality.
See RFC5893. This was one of the mistakes in IDNA2003.
I think you're right that the foregoing text is not quite correct.
And in any case, as John Klensin reiterated at the mic in a recent
PRECIS WG session, if we define something other than the Bidi Rule
then we'll likely get it wrong. I think that text predates John's
comments and hasn't been updated..
While I agree that the text that I had proposed earlier is not correct
as it stands for the reason Patrik identifies, setting it back to:
The directionality rule of a profile specifies how to treat strings
that contain right-to-left (RTL) characters (see Unicode Standard
Annex #9 [UAX9]). In general this document recommends applying the
"Bidi Rule" from [RFC5893] to strings that contain RTL characters.
(i.e., what was there before the AD Evaluation) was not correct. There
was, I thought, agreement on the problem I was pointing out, and text
inserted to address it. Encouraging the use of 5893 is a bad thing
outside of the DNS.
I think John Klensin made a good point at the mic at a semi-recent
meeting (London?) that, if we try to define a new bidirectionality rule,
we are likely to do it wrong.
As we discussed at the time, the only reason that
the 5893 Bidi Rule is so restrictive is because the (a) IDNA is already
extremely restrictive in the characters it allows and (b) for DNS
purposes, they wanted to make the display of labels around "."s more
sane. Recommending 5893 it in other contexts is far too restrictive. Let
me make another attempt to correct the above text without getting the
bit about "only LTR or RTL" wrong:
The directionality rule of a profile specifies how to treat strings
containing combinations of characters with different directionality
(e.g., left-to-right (LTR) characters, right-to-left (RTL)
characters, and/or neutral directionality characters; see Unicode
Standard Annex #9 [ UAX9 ]). A profile usually specifies a
directionality rule that restricts strings to contain combinations of
either entirely LTR and neutral characters or entirely RTL and
neutral characters. A directionality rule can also define the
allowable sequences of characters in such strings. The "Bidi Rule"
from [RFC5893] is a particularly restrictive example of such a
directionality rule.
I am not wedded to the above, but what I would hate to see was this
document go out the door with 5893 as the *recommendation*.
What I would hate to see is leaving directionality handling up to the
profiles without much guidance about what to do.
Further thoughts...
If I read your proposed text correctly, you are saying three things:
1. A profile needs to define which directionality rule applies.
2. A profile can define its own directionality rule.
3. A profile can/might/may/should use the following rule:
A string MUST contain LTR characters and neutral characters only or
contain RTL characters and neutral characters only, but MUST NOT contain
both LTR and RTL characters.
(Does that rule have a name?)
4. The directionality rule defined by a particular profile may specify
further restrictions, or may use a more restrictive rule (such as the
Bidi Rule).
I agree with (1). I think (2) is a bad idea for the reasons John
explained. I think (3) is an acceptable rule and I think we might want
to give profiles a choice between that and the Bidi Rule (thus
discouraging new directionality rules). I think (4) is a bad idea if it
assumes (2).
Peter
_______________________________________________
precis mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/precis
