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column-span and margin-collapsing (was: [CSSWG] Minutes and Resolutions 2011-09-21)

From: Håkon Wium Lie <howcome@opera.com>
Date: Mon, 26 Sep 2011 18:29:01 +0200
Message-ID: <20096.43085.472727.657197@gargle.gargle.HOWL>
To: fantasai <fantasai.lists@inkedblade.net>
Cc: "www-style@w3.org" <www-style@w3.org>
fantasai minuted:

 >    ACTION howcome: Investigate Opera's precise behavior around consecutive
 >                    colspans, to see if they match fantasai's "they're just
 >                    wrapped in an anonymous BFC" proposal is accurate.

In Opera's implementation, elements with 'column-span: all' create a
BFC as per:

   http://www.w3.org/TR/css3-multicol/#column-span

Therefore, floats are not allowed to enter a spanner in Opera's
implementation.

Spanners collapse vertically, just like these BFC-creating elements
do:

   <div style="overflow: hidden; margin: 100px 0;"></div> 
   <div style="overflow: hidden; margin: 100px 0;"></div>

As such, we think collapsing is a natural fallout from the current
spec. Therefore, I'm not sure we need to describe anonymous BFCs in
the spec.

If we decide to *not* collapse spanners, we need to change the spec,
though.

-h&kon
              Håkon Wium Lie                          CTO °þe®ª
howcome@opera.com                  http://people.opera.com/howcome
Received on Monday, 26 September 2011 16:29:38 GMT

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