W3C home > Mailing lists > Public > www-style@w3.org > August 2010

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.)

Done.

>> | 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.

Fixed.

>> | * 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.

Fixed.

>> | 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/

Fixed.

> 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.

~fantasai
Received on Thursday, 19 August 2010 18:36:34 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:20:30 GMT