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Re: [CSS21][css3-namespace][css3-page][css3-selectors][css3-content] Unicode Normalization

From: Anne van Kesteren <annevk@opera.com>
Date: Sat, 07 Feb 2009 22:50:54 +0100
To: "Phillips, Addison" <addison@amazon.com>, "Aryeh Gregor" <Simetrical+w3c@gmail.com>
Cc: "David Clarke" <w3@dragonthoughts.co.uk>, "Henri Sivonen" <hsivonen@iki.fi>, "www-archive@w3.org" <www-archive@w3.org>
Message-ID: <op.uoz4a4ec64w2qv@annevk-t60.oslo.opera.com>

On Sat, 07 Feb 2009 21:09:49 +0100, Phillips, Addison <addison@amazon.com>  
wrote:
> ... from a vendor perspective. From a specification perspective, we are  
> talking about what Selectors should do. But quite obviously Selectors is  
> only one example of the normalization issue, a point which is key in  
> I18N's official comments (under review within the WG currently).

My point is that we cannot consider Selectors standalone without knowing  
what the overall solution will be like.


>> Changing just Selectors does not solve the problem. It merely
>> fragments equality checks in implementations leading to more bugs and
>> inconsistencies. It also fragments the Web platform. If you want to
>> solve the problem you cannot just look at Selectors.
>
> Changing Selectors addresses the problem with Selectors. It doesn't  
> "solve" the overall problem. But it is one element of the problem and  
> one that is useful in discussing the problem.

That I can agree with.


>> No it is not.
>
> Probably I didn't phrase that quite right. My point is not that  
> "substring matching should be dog slow". My point is that there are  
> relative levels of acceptable performance and it is possible that  
> substring matching (such as :contains), since it used in a different way  
> than DOM tree navigation, might have different measure of "acceptable"  
> in handling normalization.

I think that any regression here in terms of speed would cause a lot of  
bad PR.


>> :contains is _highly_ sensitive to very fast equality
>> checks since CSS is live. (E.g. changes to the DOM requires checking if
>> Selectors still match or not.) In fact, precisely because of performance
>> reasons has this feature not been implemented yet in rendering engines.
>
> I don't disagree, but would then note that normalization isn't the  
> performance barrier, now is it?

It certainly complicates matters.


>> The same goes for many DOM operations.
>
> We need to resolve what the proper behavior should be ("requirements").  
> Implementations then have to meet requirements and may find diverse ways  
> to achieve. Acceptable performance is a requirement.  
> Normalization-related behavior may be. I see declarations that  
> normalization "makes things too slow" without any empirical evidence (on  
> either side) and the efforts seem to be to reject the proposed  
> requirements solely on the basis of performance.

No. The sheer complexity, and compatibility and interoperability issues  
are also reasons I have given in the various threads. Frankly, those worry  
me the most given that like you I haven't seen the actual performance  
implications yet.


> If the requirements are the right ones, then it is up to implementers to  
> create implementations that meet them (including performance  
> requirements). Balancing performance with other needs is the key here.  
> And, again, I don't believe I18N is saying that normalization must take  
> place solely at the selectors level. It is that it needs to take place  
> at the right level. This, in turn, may result in specifications (such as  
> Selectors) having conformance requirements related to normalization.

Ok.


-- 
Anne van Kesteren
<http://annevankesteren.nl/>
<http://www.opera.com/>
Received on Saturday, 7 February 2009 21:52:26 UTC

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