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Re: [css-text-4] text-wrap:balance take 2

From: Alan Stearns <stearns@adobe.com>
Date: Tue, 27 Jan 2015 19:32:26 +0000
To: Zack Weinberg <zackw@panix.com>, Tab Atkins Jr. <jackalmage@gmail.com>
CC: Florian Rivoal <florian@rivoal.net>, "www-style@w3.org" <www-style@w3.org>, Randy Edmunds <redmunds@adobe.com>
Message-ID: <1FA1A228-57FE-4D6A-AA94-6BAE0EA29739@adobe.com>
On 1/27/15, 11:00 AM, "Zack Weinberg" <zackw@panix.com> wrote:
>
>On Tue, Jan 27, 2015 at 1:19 PM, Tab Atkins Jr. <jackalmage@gmail.com> 
>wrote:
>> On Tue, Jan 27, 2015 at 12:04 AM, Florian Rivoal <florian@rivoal.net> 
>>wrote:
>>>> On 26 Jan 2015, at 23:55, Alan Stearns <stearns@adobe.com> wrote:
>>>> [...]
>>>> the deviation from the average
>>>> [...]
>>>
>>> Is this intentionally left vague, opening differences in terms of 
>>>quality of implementation?
>>
>> That's not vague.  Deviation is a numerical value that you can compare
>> across lines.  It's just linear difference.
>>
>>> I would clarify 'deviation' into 'standard deviation'. Compared to the 
>>>mean absolute deviation, the std dev is preferable, as it punishes 
>>>extreme values more. For example, on a four line block, if you have 
>>>between each line being 1 character off the average, or 2 lines being 
>>>exactly at the average and 2 lines being off by 2 characters, the 
>>>standard deviation would prefer the first situation, while the mean 
>>>absolute deviation would be indifferent.
>>
>> I agree that minimizing the squared deviation is better.  It's almost
>> always better for these kinds of "get close to the average" things.
>>
>> ~TJ
>>
>
>I am concerned that this is getting to the level of detail where we
>might end up (possibly implicitly) requiring the use of a specific
>algorithm.  I don't think that would be appropriate here.
>

I don’t think that changing the method of evaluation from 'deviation' to 
'standard deviation' gets us too close to specifying an algorithm (which I 
would definitely resist). I’ve made that change, noted that balancing 
comes before justification adjustments, and added a clause that balancing 
occurs *only if* it’s possible to get better balance than normal line 
breaking.

There will be some basic, testable cases where all reasonable attempts at 
balancing will succeed. But line-breaking algorithms differ and it’s easy 
to assemble content into difficult cases for balancing. So I assume there 
will be middle-difficulty cases where one browser balances better than 
another, and tough cases where one browser might find a way to balance 
where others fail.

Thanks,

Alan
Received on Tuesday, 27 January 2015 19:33:00 UTC

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