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Re: specifying position:sticky

From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 12 Jul 2013 18:16:49 +0100
Message-ID: <51E03A01.1090503@exyr.org>
To: www-style@w3.org
Le 12/07/2013 17:37, Corey Ford a écrit :
> I've been working on specification text for sticky positioning
> (previously discussed starting at [1], and currently implemented in
> WebKit) that I'd be interested in feedback on:
>
> [1] http://lists.w3.org/Archives/Public/www-style/2012Jun/0627.html
>
>
> A sticky positioned box is first laid out in the normal flow (equivalent
> to position: static). The box may be repositioned as follows, but as
> with relative positioning, any repositioning does not affect the box
> that follows.
>
> The box's position depends on its containing block (established as for
> position:static) as well as its scrolling container, defined by the
> nearest ancestor in the same document with a computed value for
> 'overflow-x' or 'overflow-y' other than 'visible', or the viewport if no
> such ancestor exists.
>
> For any of 'top', 'bottom', 'left', and 'right' that are not 'auto', if
> the box's normal position would cause that edge of its margin box to be
> less than the specified distance within that paddingedge of its
> scrolling container, the box is repositioned to that distance from the
> edge, such that the box doesnot move while the container scrolls. The
> distance the box is repositioned is limited such that the element's
> margin box never crosses the oppositeedge of the content box of its
> containing block, with the effect thatthe element starts scrolling with
> its container again when it reaches the end of its containing block.(If
> 'top', 'bottom', 'left', and 'right' are all 'auto', the effect will be
> identical to relative positioning with those values). None of these
> properties affect the width or height of the element. Percentage values
> of these properties reference the padding box of the scrolling container.
>
> If both 'top' and 'bottom' are not 'auto' and the element's margin box
> is taller than the padding boxheight of the scrolling container minus
> the sum of 'top' and 'bottom', then only 'top' is considered and
> 'bottom' is ignored. Similar logic applies for 'left' and 'right' with
> widths, except that if the 'direction' property of the containing block
> is 'ltr', 'right' is ignored, and if it is 'rtl', 'left' is ignored.
>
> Note: Sticky positioned elements are considered 'positioned', so are
> z-ordered according to the same rules asrelatively positioned elements,
> and establish the containing block of absolutely positioned descendants.
> Sticky positioning(like relative positioning)does not affect the
> computed value of 'display' as position:absolute does (so does not force
> an inline element to be displayed as block).

+1, this looks like a reasonable definition.

-- 
Simon Sapin
Received on Friday, 12 July 2013 17:17:00 UTC

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