On 2/9/15 1:56 PM, Peter Saint-Andre - &yet wrote:
On 2/9/15 10:20 AM, Pete Resnick wrote:
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*.
Further thoughts...
If I read your proposed text correctly, you are saying three things:
1. A profile needs to define which directionality rule applies.
Yep. I wish we didn't have to say that (because this is about display,
not processing), but I am definitely in the rough about being able to
say "mixed-direction is fun; have at it!".
2. A profile can define its own directionality rule.
Well, we have given that ability, but I don't think it's a good idea for
a profile to do so. SHOULD NOT.
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.
As Klensin points out to me out of band, I screwed that up too, since
some digits and punctuation are LTR but would certainly violate the
Principle of Least Astonishment if we disallowed them alongside RTL
characters. So at the very least, I am going to chew on this with John
for a bit and see if there *is* some simple formulation of a
directionality rule short of 5893.
(Does that rule have a name?)
"Pete's lousy attempt to formulate a simple rule"?
Consider this on hold.
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).
Same as 2 above. We've given them the ability to do so, but it would be
a really bad idea if they did. SHOULD NOT.
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).
Yep.
This might turn out that I'm convinced there is nothing better to say
than "use 5893". That will cause me to weep into my beer. But give me a
bit to chat with Klensin and we'll see if we can come up with sanity.
(*Sigh*)
pr
--
Pete Resnick<http://www.qualcomm.com/~presnick/>
Qualcomm Technologies, Inc. - +1 (858)651-4478
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