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Re: bidi embedding for block-level elements

From: Asmus Freytag <asmusf@ix.netcom.com>
Date: Fri, 23 Jul 2010 17:14:31 -0700
Message-ID: <4C4A3067.8050507@ix.netcom.com>
To: fantasai <fantasai.lists@inkedblade.net>
CC: Ian Hickson <ian@hixie.ch>, Simon Montagu <smontagu@smontagu.org>, www-html@w3.org, 'WWW International' <www-international@w3.org>, "public-i18n-core@w3.org" <public-i18n-core@w3.org>, "www-style@w3.org" <www-style@w3.org>
On 7/23/2010 4:52 PM, fantasai wrote:
> On 07/23/2010 04:16 PM, Asmus Freytag wrote:
>> The ceiling on embeddings in the bidi algorithm was invented in an
>> attempt to prevent implementations from taking shortcuts and setting
>> their own ceiling. 60 some levels was thought to be small enough that
>> any implementation could handle it, and yet inconceivably large for
>> practical cases. However, the limit is on bidi levels, not on the number
>> of embeddings. It occurs to me that in some contexts, levels could
>> increment by 2. Might be worth someone checking in the bidi
>> specification under what circumstances that occurs, and whether that
>> means the worst case nesting limit is lower.
>
> UAX9 applies that limit only to explicit embedding levels.
>   http://unicode.org/reports/tr9/#BD2
>   http://unicode.org/reports/tr9/#X1
> As you say, implicit levels can increase the base number by two.
> Capping the explicit levels at 61 leaves just enough room in a
> 6-bit integer space to handle implicit codes.
Yes, implicit levels can go slightly higher on top of the highest 
explicit embedding,
but the discussion here is about embeddings that are equivalent to 
explicit embeddings.

A./
Received on Saturday, 24 July 2010 00:15:07 GMT

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