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[Bug 16037] Margin collapsing: unintuitive collapsing between last child and auto-height, large min-height parent

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Date: Mon, 20 Feb 2012 19:39:03 +0000
To: public-css-bugzilla@w3.org
Message-Id: <E1RzZ4h-0005bn-KF@jessica.w3.org>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=16037

--- Comment #1 from Anton P <antonsforums@yahoo.co.uk> 2012-02-20 19:39:01 UTC ---
David Baron felt that preventing those margins from collapsing (or at least,
making the behaviour undefined) when there is a non-zero min-height might be
the way to go, but noted that implementations do fairly consistently collapse
those margins. [http://lists.w3.org/Archives/Public/www-style/2010Sep/0451.html
, http://lists.w3.org/Archives/Public/www-style/2011Mar/0346.html]

At the F2F in Paris 2012
[http://lists.w3.org/Archives/Public/www-style/2012Feb/0529.html] Alex
Mogilevsky argued that implementers have resisted conditional margin collapsing
that depends on whether min-height has an effect or not, since all other
aspects of margin collapsing can be calculated before layout starts but not
this one.  He also argued that we don't want to prevent margin collapsing when
min-height didn't take effect (which, quite apart from being undesirable for
authors, could also result in cycles since whether or not the min-height has an
effect depends on whether or not the parent is expected to contain its child's
margin).

The solution would seem to be to always permit collapsing even in the "strange"
case.

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