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Re: [CSS Intrinsic & Extrinsic Sizing] sizing of absolutely positioned elements

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 9 Oct 2012 13:55:04 -0700
Message-ID: <CAAWBYDCVXYc9Mz0nk=cLGvTeNKVQ+iCeqDSBwYN5LfompvWVDg@mail.gmail.com>
To: Ojan Vafai <ojan@chromium.org>
Cc: www-style@w3.org
On Fri, Sep 7, 2012 at 3:30 PM, Ojan Vafai <ojan@chromium.org> wrote:
> http://www.w3.org/TR/CSS2/visudet.html#containing-block-details
> "If the element has 'position: absolute', the containing block is
> established by the nearest ancestor with a 'position' of 'absolute',
> 'relative' or 'fixed', in the following way:
> In the case that the ancestor is an inline element, the containing block is
> the bounding box around the padding boxes of the first and the last inline
> boxes generated for that element. In CSS 2.1, if the inline element is split
> across multiple lines, the containing block is undefined.
> Otherwise, the containing block is formed by the padding edge of the
> ancestor."
> http://dev.w3.org/csswg/css3-sizing/#extrinsic-sizing
> "less the box's inline-axis margins, borders, and padding."
> Should the extrinsic size of position:absolute elements include the padding
> or not? My feeling is that it shouldn't for the purposes of things like
> fill-available and auto-sizing perpendicular writing-modes, but I could be
> convinced otherwise.

Nothing to change here, luckily - you just misread that section. ^_^

The m/b/p that you're subtracting is the abspos's *own* m/b/p, because
we are specifically defining the *inner* size.  The containing block
doesn't have anything subtracted.

> Not that we can change it now, but it's not clear to me why CSS2 chose the
> padding box in the first place. What's the use-case this addresses?

fantasai thinks that this was because of compat issues.

~TJ and fantasai
Received on Tuesday, 9 October 2012 20:55:51 UTC

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