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Re: [CSS2.1] Clarifying 8.3.1 Collapsing Margins

From: fantasai <fantasai.lists@inkedblade.net>
Date: Thu, 19 Aug 2010 11:35:59 -0700
Message-ID: <4C6D798F.9080808@inkedblade.net>
To: Anton Prowse <prowse@moonhenge.net>
CC: "www-style@w3.org" <www-style@w3.org>
On 08/18/2010 12:25 PM, Anton Prowse wrote:
> On 18/08/2010 10:11, fantasai wrote:
>> This is for CSS2.1 Issue 159
>> http://wiki.csswg.org/spec/css2.1#issue-159
>> triggered by this email
>> http://lists.w3.org/Archives/Public/www-style/2010Feb/0015.html
>> This is version 2.
> The margins may not be mutually adjoining (indeed, frequently won't be
> now that the concept is intransitive) yet they may still collapse. The
> sentence needs reformulating in terms of collapsing. (Not easy to do
> elegantly, unfortunately.)


>> | Horizontal margins never collapse.
>> | The above rules imply that:
> [...]
>> | * The bottom margin of an in-flow block element with a
>> | 'height' of 'auto' collapses with its last in-flow block-level
>> | child's bottom margin if the element has no bottom padding or
>> | border.
> ...unless the child has clearance and its top and bottom margins are
> adjoining.


>> | * An element's own margins collapse if the 'min-height' property
>> | is zero, and it has neither top or bottom borders nor top or
>> | bottom padding, and it has a 'height' of either 0 or 'auto', and
>> | it does not contain a line box, and all of its in-flow children's
>> | margins (if any) are adjoining.
> This is confusing; "(if any)" qualifies children, not margins.

I'm making it informative, so it doesn't particularly matter.

> Also, as above, "adjoining" no longer covers all desired cases. The
> sentence needs reformulating in terms of collapsing.


>> | If the top and bottom margins of a box are adjoining, then it is
>> | possible for margins to collapse through it. In this case, the
>> | position of the element depends on its relationship with the other
>> | elements whose margins are being collapsed. [...]
> As above:
> s/are adjoining/collapse/
> and, for readability,
> s/for margins/for other margins/


> Anyhow, this sentence was never correct, since there may not be any
> other margins involved and so the applicability of this part is not just
> restricted to "this case". Really, the whole sentence needs changing:

The sentence is correct. Even if no other elements are involved,
the element's own top and bottom margins do collapse through its
own box.

Received on Thursday, 19 August 2010 18:36:34 UTC

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