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Re: [CSS21] Issue 70 (collapsing margins and block formatting contexts)

From: fantasai <fantasai.lists@inkedblade.net>
Date: Mon, 29 Dec 2008 13:30:01 -0800
Message-ID: <49594159.4060709@inkedblade.net>
To: Anton Prowse <prowse@moonhenge.net>
CC: "www-style@w3.org" <www-style@w3.org>

Anton Prowse wrote:
> 
> Resulting from discussion in the face-to-face on 2008-08-22,[1, 2] a 
> decision was made to change 8.3.1 to state that vertical margins of 
> block formatting contexts do not collapse with their in-flow 
> children.[3]  (Apparently this arose from discussion of Issue 14.[4])
> 
> Prior to the decision, it was well-known (if not explicitly mandated) 
> that block formatting contexts were /not/ excluded from such margin 
> collapsing.[5]
> 
> To my knowledge this change wasn't discussed on this mailing list, and 
> whilst I have no objection to the decision I would be interested to hear 
> the thoughts of those involved in it, as it has a direct impact on 
> recently-discussed ideas on a possible need for in-flow block-level 
> neutral block formatting contexts.[6]

As Hixie notes, margins don't collapse for any of the current block
formatting context roots. Or at least, we believed that should be
the case. IIRC several missed exceptions were found. To avoid
unintentionally excluding any other types of boxes from that list
we decided to issue a blanket statement about block formatting
contexts in general.

 > possible need for in-flow block-level neutral block formatting
 > contexts.[6]
 > [6] http://lists.w3.org/Archives/Public/www-style/2008May/0262.html

There was a proposed clear-after property that I believe would
have the effect you're looking for.
   http://www.w3.org/TR/2002/WD-css3-box-20021024/#the-clear-after

~fantasai
Received on Monday, 29 December 2008 23:29:02 GMT

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