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RE: [CSS21] Does the root element establish a block formatting context? (was: Re: [CSS21] 9.2 Anonymous boxes)

From: Arron Eicholz <Arron.Eicholz@microsoft.com>
Date: Mon, 14 Mar 2011 20:30:28 +0000
To: Anton Prowse <prowse@moonhenge.net>
CC: "www-style@w3.org" <www-style@w3.org>
Message-ID: <07349ECFC3608F48BC3B10459913E70B12CFD324@TK5EX14MBXC132.redmond.corp.microsoft.com>
On Monday, August 09, 2010 3:31 AM Anton Prowse wrote:
> > fantasai wrote:
> >> On 08/01/2010 02:45 PM, Anton Prowse wrote:
> >>> Issue 5:
> >>>
> >>> Why would there be an anonymous block box around the BODY? Surely
> >>> the principal block box of the (implied[6]) HTML is what surrounds
> >>> the anonymous block box around C1, the principal block box of the P,
> >>> and the anonymous block box around C2.
> >>
> >> Good point. Assuming "display: none" for the <head> and "display: block"
> >> for <html>, the example here is wrong.
> >
> > Yep.  And just to be clear here, had HTML been display:inline, we'd
> > have ended up with the three block boxes as the "top level" boxes of
> > the canvas, since there's no "initial box" or similar concept, right?
> > (There's an initial containing block, but this is a region, not a
> > box.)
> 
> Nope, I'm wrong (in CSS21 at least).  Whilst there's no "initial box", the
> computed value of 'display' for the root element is either 'table', 'block' or
> 'list-item' (9.7).  Hence it always generates a principal box.
> 
> Which is a relief, really – because shouldn't the root element establish a block
> formatting context?  (It was believed to do so in 2002.[1]) It doesn't if its
> specified value is 'inline' or 'run-in', for example (in which case its computed
> value of 'display' is 'block').  Indeed, 9.4.1 seems to explicitly exclude the
> possibility:
> 
>    # Floats, absolutely positioned elements, inline-blocks, table-cells,
>    # table-captions, and elements with 'overflow' other than 'visible'
>    # (except when that value has been propagated to the viewport)
>    # establish new block formatting contexts.
> 
> But I'm not sure things make much sense without an initial block formatting
> context.  (At least, further editorial work seems necessary in 9.2.1 if there
> isn't, since, as far as I can currently tell, the definition of "block-level box" is
> roughly "a box which participates in a block formatting context".)
> 
> Note that the root element possesses all the characteristic properties of an
> element which establishes a BFC, including in relation to margin collapsing.
> 

Thank you for your feedback. The CSSWG resolved not to make changes to the CSS 2.1 specification[1]. We will be reevaluating this issue for errata and future versions of CSS. 

Please respond before 18 March, 2011 if you do not accept the current resolution.

[1] http://w3.org/TR/CSS

Received on Monday, 14 March 2011 20:31:04 GMT

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