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[css3-multicol] margin collapsing between column-spanning element and blocks in column boxes: if, when?

From: Gérard Talbot <www-style@gtalbot.org>
Date: Sat, 14 Sep 2013 16:09:52 -0400
Message-ID: <6117ba064925f8487c26d8afec4df1c4.squirrel@ed-sh-cp3.entirelydigital.com>
To: "Håkon Wium Lie" <howcome@opera.com>
Cc: "W3C www-style mailing list" <www-style@w3.org>
Håkon,

One issue that I wish would be explicit and clarified in the spec is if
margin collapsing can occur between a column-spanning element and blocks
in column boxes. If it can occur, then the spec should say so, then define
under which conditions along with an example. If it does not occur, then
the spec should say so.

Here's a test where browsers differ:

http://www.gtalbot.org/BrowserBugsSection/CSS3Multi-Columns/Opera/NewTests/multicol-spanning-margin-collapsing-234.xht

(
This test is a modified and customized test from Example XX in
http://www.w3.org/TR/css3-multicol/#column-span
and in Example 22 in
http://dev.w3.org/csswg/css-multicol/#column-span
)

Firefox 23 does not support column-span: all, so here, I am only taken
into consideration IE10, IE11 (preview), Chrome 29.0.1547.65 and Opera
12.16.

The issue involves the margin collapsing of the margin-bottom of the
h2#column-spanning which is 80px with the margin-top (which is 40px) of
the p in first column box.

If margin collapsing occurs between those 2 margins, then there should be
an 80px (max(80px, 40px)) tall blue area. IE10 and IE11 do that. (Prince9
also does that but it fails to render the margin-top of first p.)

If margin collapsing does not occur (because it should not occur) between
those 2 margins, then there should be an 120px (80px + 40px) tall blue
area. Chrome 29.0.1547.65 and Opera 12.16 do that.

If margin collapsing can occur between column-spanning element and blocks
in column boxes, then it could be possible to create tests where several
blocks' margin-top collapses with a preceding-sibling column-spanning
element.

If margin collapsing can occur between column-spanning element and blocks
in column boxes, then it could be also possible to create tests where
several blocks' margin-bottom collapses with a following-sibling
column-spanning element.

Another sub-issue is: can margin collapsing occur between 2
vertically-adjacent (following sibling) column-spanning elements.

Gérard
-- 
CSS 2.1 Test suite RC6, March 23rd 2011
http://test.csswg.org/suites/css2.1/20110323/html4/toc.html

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Received on Saturday, 14 September 2013 20:10:23 UTC

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