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Re: bidi embedding for block-level elements

From: fantasai <fantasai.lists@inkedblade.net>
Date: Fri, 23 Jul 2010 16:52:08 -0700
Message-ID: <4C4A2B28.4070508@inkedblade.net>
To: Asmus Freytag <asmusf@ix.netcom.com>
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 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.

~fantasai
Received on Friday, 23 July 2010 23:52:46 GMT

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