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[Bug 16072] New: Margin collapsing: clarification needed as to where a collapsed margin manifests itself

From: <bugzilla@jessica.w3.org>
Date: Wed, 22 Feb 2012 08:30:01 +0000
To: public-css-bugzilla@w3.org
Message-ID: <bug-16072-5148@http.www.w3.org/Bugs/Public/>

           Summary: Margin collapsing: clarification needed as to where a
                    collapsed margin manifests itself
           Product: CSS
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: CSS Level 2
        AssignedTo: bert@w3.org
        ReportedBy: antonsforums@yahoo.co.uk
         QAContact: public-css-bugzilla@w3.org

Reported by Anton Prowse

The spec currently says that the bottom margins collapse for an auto-height,
non-BFC parent with large min-height and a last in-flow non-self-collapsing
child, even when the parent's used height is larger than the total height of
all of its content and its last child's bottom margin.  The WG feels that this
is acceptable behaviour because the alternatives are worse in a world without
partial margin collapsing.  (See Bug 16037.)

However, nothing in the spec indicates where the collapsed margin should
manifest itself.  (See also Bug 15894 - Position of top content edge of
non-replaced block-level elements is not clearly defined.)  This problem has
always existed, although in most cases it's intuitive that the collapse margin
should manifest itself outside the parent's border box.  However, in the case
described above, it's less intuitive, since one could argue that the collapsed
margin might manifest itself immediately outside the /child's/ border box, for

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Received on Wednesday, 22 February 2012 08:30:03 UTC

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