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[CSS 2.1] [Section 8.3.1] Margin collapsing and top: auto (abs. pos)

From: Gérard Talbot <www-style@gtalbot.org>
Date: Mon, 2 Aug 2010 14:57:37 -0700
Message-ID: <99716a117eab39a20ba4a70870735655.squirrel@cp3.shieldhost.com>
To: "www-style@w3.org" <www-style@w3.org>
Hello all,

Are abs. pos. and fixed pos. elements taken out of normal flow before
margin collapsing occurs or are abs. pos. and fixed pos. elements taken
out of normal flow after margin collapsing occurs?

Testcase (self-explanatory and reduced)
--------

http://www.gtalbot.org/BrowserBugsSection/css21testsuite/margin-collapsing-and-abs-pos.html


Spec says:
"
The bottom margin of an in-flow block-level element is always adjoining to
the top margin of its next in-flow block-level sibling, unless that
sibling has clearance.
"
http://www.w3.org/TR/CSS21/box.html#collapsing-margins

Now, "next in-flow block-level sibling" could mean not just n+1th sibling
but n+2th sibling, n+3th sibling, n+kth sibling: this is where
interpretation/exegesis seems critical, decisive.

I am 90% sure that Opera 10.x mishandles that testcase and that others
(IE8, Firefox 3.x, Chrome 5.x, Safari 5.x, Konqueror 4.x) handle it
correctly.

The list of steps in E.2 Painting Order
http://www.w3.org/TR/CSS21/zindex.html#painting-order
seems to suggest that margin collapsing will be executed, processed when
dealing with all in-flow, non-positioned, block-level descendants in tree
order.

The testcase I created comes from a reduction of

http://test.csswg.org/suites/css2.1/20100727/html4/abspos-021.htm

http://www.hixie.ch/tests/adhoc/css/box/absolute/020.html

http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/061.html

I have searched for posts in the mailing which would have covered that
particular issue and did not find any.

I have also searched the list of opened issues wrt CSS 2.1:
http://wiki.csswg.org/spec/css2.1#css21

regards, Gérard
-- 
CSS 2.1 Test suite beta 2 (July 27th 2010)
http://test.csswg.org/suites/css2.1/20100727/html4/toc.html

Contributions to CSS 2.1 test suite
http://www.gtalbot.org/BrowserBugsSection/css21testsuite/

Web authors' contributions to CSS 2.1 test suite
http://www.gtalbot.org/BrowserBugsSection/css21testsuite/web-authors-contributions-css21-testsuite.html
Received on Monday, 2 August 2010 21:58:14 GMT

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