Re: per-paragraph auto-direction, a.k.a. dir=uba

A few comments on Aharon's proposal.

1) Aharon wrote: "autodirmethod inherits; dir does not. The default would 
probably be first-strong."
What do you mean, "dir does not" (inherit)?  I interpret it as: an inner 
element without an explicit dir attribute does not inherit its direction 
from outer elements. So where does it get it from?
I am sure it is not the right interpretation, but I am afraid the text 
itself is not very clear.

2) Aharon wrote: "The first-strong algorithm returns the direction of the 
first strong (L, AL, or R) character it encounters. If it does not 
encounter any, it returns ltr if it encounters any weak ltr characters (EN 
or AN)"
I think that AN should rather return rtl (in UBA jargon, EN digits in a 
neutral context receive bidi embedding level 0 while AN digits receive 
level 2). Native Arabic users should confirm.

3) I may have missed it, but the description of dir=auto with 
autodirmethod=uba nowhere specifies that the direction is recomputed for 
each new paragraph (or element of such and such types).


Shalom (Regards),  Mati
           Bidi Architect
           Globalization Center Of Competency - Bidirectional Scripts
           IBM Israel
           Phone: +972 2 5888802    Fax: +972 2 5870333    Mobile: +972 52 
2554160




From:   "Aharon (Vladimir) Lanin" <aharon@google.com>
To:     Matitiahu Allouche/Israel/IBM@IBMIL
Cc:     fantasai <fantasai.lists@inkedblade.net>, "Phillips, Addison" 
<addison@lab126.com>, Adil Allawi <adil@diwan.com>, Behdad Esfahbod 
<behdad@behdad.org>, Ehsan Akhgari <ehsan@mozilla.com>, 
public-i18n-bidi@w3.org, public-i18n-bidi-request@w3.org, Shachar Shemesh 
<shachar@shemesh.biz>
Date:   14/09/2010 17:39
Subject:        Re: per-paragraph auto-direction, a.k.a. dir=uba



I second Mati's proposal. As Ehsan has pointed out <textarea readonly> can 
be used to display plain text (as opposed to edit it), even though 
somewhat awkwardly. And if we work out a bigger proposal, we can tweak the 
bugs filed on HTML5 and CSS3. Right now it is imperative to produce a new 
draft of the proposal and file the bugs (October 1 deadline for HTML5..., 
apparently).

I do want to put dir=uba under the dir=auto umbrella, via 
autodirmethod=first-strong|any-rtl|uba. autodirmethod inherits; dir does 
not. The default would probably be first-strong.

Is this agreeable to everyone? Please respond.

Here is a quick spec for dir=auto:
Using dir=auto with autodirmethod=first-strong|any-rtl would:
Make the default value for the ubi attribute ubi (i.e. on), as described 
elsewhere.
Set the CSS direction to ltr or rtl according to the indicated algorithm.
Invoke the indicated algorithm on the in-order traversal of the descendent 
text nodes, with the following exceptions:
Text nodes under a descendant element with an explicit dir attribute 
(including dir=auto).
The part of the text after the first X characters (where the text in nodes 
excluded above are not part of the count). Do we need this? If so, what's 
a good X value? 100?
Parts of the text between an LRE, RLE, LRO, RLO, and its matching PDF.
The first-strong algorithm returns the direction of the first strong (L, 
AL, or R) character it encounters. If it does not encounter any, it 
returns ltr if it encounters any weak ltr characters (EN or AN). If it 
does not encounter any of those either, it returns the inherited 
direction.
The any-rtl algorithm returns rtl if it encounters any strong RTL 
character, or ltr otherwise.
Using dir=auto with autodirmethod=uba would (by default) set unicode-bidi 
to "uba" and direction according to first-strong. (Note that this includes 
leaving direction at the inherited value if the content is neutral.)
For elements other than <textarea>, unicode-bidi:uba is treated as 
unicode-bidi:isolate.
On <textarea>, unicode-bidi:uba means that:
The UBA on the textarea content is invoked specifying only a default 
paragraph level (in icu4j terminology, either LEVEL_DEFAULT_LTR or 
LEVEL_DEFAULT_RTL), based on the the element's own direction value as 
calculated above. (This makes the all-neutral paragraphs use the same 
direction as the first paragraph that is not all-neutral.)
Each UBA paragraph’s lines’ alignment is determined by the paragraph’s 
resolved base level when the element's text-align is start or end.

Aharon


On Tue, Sep 14, 2010 at 2:21 PM, Matitiahu Allouche <matial@il.ibm.com> 
wrote:
I don't feel competent enough to find the magic solution for all the 
questions that dir=uba seems to raise.  This discussion has been going on 
for a while, and there is real danger that the whole item be shelved if a 
consensus is not found soon. 

However, based on the discussion on the list, I think that the following 
points are more or less agreeable to all: 
1) dir=uba is mostly needed for <pre> and <textarea> elements. 
2) All or most of the problems are related to using dir=uba with <pre>. 
3) There are alternatives to using dir=uba with <pre> for multiple 
paragraphs, like separating the text in distinct paragraphs. 
4) There is no problem related to using dir=uba with <textarea>. 
5) There is no other way than dir=uba to achieve paragraph-based direction 
for <textarea>. 

Given the above, I am suggesting to at least allow dir=uba for <textarea>, 
even if its use for other types of elements is postponed or abandoned 
altogether. 


Shalom (Regards),  Mati
          Bidi Architect
          Globalization Center Of Competency - Bidirectional Scripts
          IBM Israel
          Phone: +972 2 5888802    Fax: +972 2 5870333    Mobile: +972 52 
2554160