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RE: [CSS21] 9.4.1 (Block formatting contexts) Definition - comments on Working Draft

From: Arron Eicholz <Arron.Eicholz@microsoft.com>
Date: Wed, 16 Mar 2011 22:42:21 +0000
To: Anton Prowse <prowse@moonhenge.net>
CC: "www-style@w3.org" <www-style@w3.org>
Message-ID: <07349ECFC3608F48BC3B10459913E70B12D1574C@TK5EX14MBXC132.redmond.corp.microsoft.com>
On Friday, January 07, 2011 12:51 PM Anton Prowse wrote:
> An editorial suggestion:
> 
> 9.4.1 (Block formatting contexts) says:
> 
>    # Floats, absolutely positioned elements, block containers (such as
>    # inline-blocks, table-cells, and table-captions) that are not block
>    # boxes, and block boxes with 'overflow' other than 'visible' (except
>    # when that value has been propagated to the viewport) establish new
>    # block formatting contexts.
> 
> and 11.1.1 (Overflow: the 'overflow' property) says:
> 
>    # UAs must apply the 'overflow' property set on the root element to
>    # the viewport. When the root element is an HTML "HTML" element or an
>    # XHTML "html" element, and that element has an HTML "BODY" element
>    # or an XHTML "body" element as a child, user agents must instead
>    # apply the 'overflow' property from the first such child element to
>    # the viewport, if the value on the root element is 'visible'. The
>    # 'visible' value when used for the viewport must be interpreted as
>    # 'auto'. The element from which the value is propagated must have a
>    # used value for 'overflow' of 'visible'.
> 
> So in fact if a block box whose 'overflow' other than 'visible' has been
> propagated to the viewport then its used value is 'visible' and so it's no longer
> under consideration is 9.4.1.  In other words, 9.4.1 can be clarified as follows:
> 
> s/block boxes with 'overflow' other than 'visible' (except when that value has
> been propagated to the viewport)/block boxes with used value of 'overflow'
> other than 'visible'/
> 
> The change from (presumably) computed value to used value in 9.4.1
> shouldn't cause any implementation difficulties because for all block boxes
> whose 'overflow' isn't propagated, the used value can only be other than
> visible if the computed value is also other than visible.
> Hence under my proposed change, it's known whether the block box
> establishes a BFC as soon as the computed value is calculated, just as it is with
> the current spec.
> 
> I find 9.4.1 much easier to parse under this proposed change, not least
> because it strengthens the separation of Ch.11 from Ch.9.
> 
> Note that under both formulations, the root element doesn't establish a
> block formatting context.  This is conceptually questionable and is the subject
> of Issue 209.
> 

Thank you for your feedback. The CSSWG resolved not to make these 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 Wednesday, 16 March 2011 22:42:54 GMT

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