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[Bug 17130] New: Margin collapsing: clarify the transitivity

From: <bugzilla@jessica.w3.org>
Date: Mon, 21 May 2012 10:46:33 +0000
To: public-css-bugzilla@w3.org
Message-ID: <bug-17130-5148@http.www.w3.org/Bugs/Public/>

           Summary: Margin collapsing: clarify the transitivity
           Product: CSS
           Version: unspecified
          Platform: PC
        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

8.3.1 says:

  # In CSS, the adjoining margins of two or more boxes (which might or
  # might not be siblings) can combine to form a single margin. Margins
  # that combine this way are said to collapse, and the resulting
  # combined margin is called a collapsed margin.
  # Adjoining vertical margins collapse, except:
  #  [omitted cases]

  # A collapsed margin is considered adjoining to another margin if any
  # of its component margins is adjoining to that margin.
  # Note. Adjoining margins can be generated by elements that are not
  # related as siblings or ancestors.

This recently-rewritten text has made a clear distinction between adjointness
and margin collapsing, employing the former as a tool to define the latter. 
This was a good idea, but it doesn't quite achieve its goals: there still
remains some vagueness about whether either concept is transitive.

Note there doesn't seem to be any particular advantage in making adjointness
transitive, and the disadvantage is that it becomes a less useful tool for
defining collapsing since it becomes too similar to collapsing.  (8.3.1 is a
pretty hard section to word satisfactorily, so the more useful the tool, the

I propose we make it clearer that adjointness is non-transitive and collapsing
is transitive.

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Received on Monday, 21 May 2012 10:46:59 UTC

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