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Errata and ED (was:: [css3-flexbox] Children of flex items ignoring cross-axis percentage length)

From: Simon Sapin <simon.sapin@exyr.org>
Date: Wed, 09 Apr 2014 10:53:50 +0100
Message-ID: <534518AE.5020606@exyr.org>
To: "Tab Atkins Jr." <jackalmage@gmail.com>, Daniel Holbert <dholbert@mozilla.com>
CC: Greg Whitworth <gwhit@microsoft.com>, fantasai <fantasai@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>, "mstensho@opera.com" <mstensho@opera.com>, "ojan@chromium.org" <ojan@chromium.org>
On 09/04/2014 01:16, Tab Atkins Jr. wrote:
> On Mon, Apr 7, 2014 at 10:36 AM, Daniel Holbert <dholbert@mozilla.com> wrote:
>> Interesting.
>>
>> Here's a perhaps simpler case: suppose a vertical flex container has a
>> flex item with "height: 10px; flex-basis: 50px", and that flex item has
>> a child with a percent-valued height.
>>
>> Should the percent height resolve against the 10px specified-height, or
>> against the flex-basis (which we can reliably know ahead of time is what
>> its used height will end up resolving to)?
>>
>> Testcase: http://jsfiddle.net/LcL8U/
>>
>> CSS21 says this about percent height values:
>>    # The percentage is calculated with respect to the
>>    # height of the generated box's containing block.
>>    # If the height of the containing block is not
>>    # specified explicitly (i.e., it depends on content
>>    # height), and this element is not absolutely
>>    # positioned, the value computes to 'auto'."
>> http://www.w3.org/TR/CSS21/visudet.html#propdef-height
>>
>> (We can disregard the second half of this spec text here, since there's
>> clearly no dependence on content in my or Greg's example, and no browser
>> seems to be treating the percent height as "auto".)
>
> Sigh, bad application of errata strikes again!  (We errata'd that to
> happen at used-value time instead.)

Daniel, you may want to look at the ED, which has errata applied:

http://dev.w3.org/csswg/css2/

(This exact bit was actually missing, but I fixed it yesterday and went 
through the rest of the CSS 2 errata to double-check the ED.)

When looking at /TR, readers are apparently expected to look at the 
errata document at all times and do mental the substitution themselves. 
This just doesn’t work IMO.


>> So the question is, what is the "height of the box's containing block".
>> Blink seems to be saying it's the specified "height" property, while
>> Gecko/Trident are using the actual box's height (the flex basis). Since
>> the CSS21 spec text [quoted above] seems to be talking about box height
>> rather than the "height" property here, I tend to think the
>> Gecko/Trident behavior is correct.
>
> Yes, it's the actual height (the flex basis).  I think the spec is
> clear about this, but I can correct something if it's not.


-- 
Simon Sapin
Received on Wednesday, 9 April 2014 09:54:27 UTC

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