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Re: [css2.1] Issue 158 and Issue 178 Resolution

From: Anton Prowse <prowse@moonhenge.net>
Date: Wed, 18 Aug 2010 23:32:04 +0200
Message-ID: <4C6C5154.6080204@moonhenge.net>
To: www-style list <www-style@w3.org>
CC: fantasai <fantasai.lists@inkedblade.net>, "Tab Atkins Jr." <jackalmage@gmail.com>
On 18/08/2010 20:13, fantasai wrote:
> On 08/18/2010 11:00 AM, Anton Prowse wrote:
>> On 18/08/2010 01:09, fantasai wrote:
>>> On 08/14/2010 11:02 PM, Anton Prowse wrote:
>>>> > * The amount necessary to place the top border edge of the block
>>>> > even with the previously computed hypothetical position of the top
>>>> > border edge of the element. (Informative Note: This is necessary to
>>>> > handle the case where the float moves due to the element's top
>>>> > margin no longer collapsing with previous margins.)
>>>> (This is assuming – reasonably, I think – that that's what the equation
>>>> in Calculation 2 really is trying to say.)
>>> We do know, based on the CSSWG's archives, that the rewording above
>>> is the original intent of Calculation 2. I had in fact suggested
>>> replacing Ian's rather convoluted calculation with the following
>>> at that time:
>>> | 2. The amount necessary to place the border edge of the block
>>> | at its hypothetical position.
>>> The intent is exactly to ensure that the clearing element does not
>>> move upwards as a result of clearing.
>> Hmm, I went through the public mailing list archives in some detail
>> prior to participating in this clearance discussion, and didn't find
>> anything. Are you referring to non-public archives? If so, would you
>> be able and willing to post any or all of this discussion publicly?
>> Anyhow, thanks for the info. I'll proceed to factor this into my recent
>> analysis.
> This was in the non-public archives, back when the CSSWG conducted
> technical discussion on a Members-only list. The tests that factored
> into that decision were these:
>   http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/microsoft/

OK, thanks.

Unfortunately those test cases are not very comprehensive.  (And there's
nothing more advanced in the CSS21 Test Suite Beta 3.)  In particular,
there's nothing testing the more challenging cases, neither similar to
the (not especially scary) one I've been using to demonstrate the spec
strangeness in [1,2] nor any involving self-collapsing elements with
non-trivial self-collapsing children.

Once we've resolved the clearance issues, I'd be happy to prepare and
submit a couple of formal tests for these cases if you'd like.

Judging from your comments, it looks very much as if the spec should be
interpreted as in [2]:

On 17/08/2010 20:35, Anton Prowse wrote:
> [...] the need for clearance is decided by effectively
> ignoring the top margin of the clearing element's child, and then the
> clearing element is moved to below the float /also/ as if the child's
> margin were non-existent.  Hence the clearance concept would be rather
> peculiar – and very aggressive towards child top margin – under the
> interpretation discussed in this post.

To me, this is a spec error (unrelated to issue 158).

[1] http://lists.w3.org/Archives/Public/www-style/2010Aug/0276.html
[2] http://lists.w3.org/Archives/Public/www-style/2010Aug/0309.html

Anton Prowse
Received on Wednesday, 18 August 2010 21:34:16 UTC

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