W3C home > Mailing lists > Public > www-style@w3.org > July 2013

Re: specifying position:sticky

From: Simon Fraser <smfr@me.com>
Date: Fri, 12 Jul 2013 10:46:01 -0700
Cc: www-style@w3.org
Message-id: <2CF14CAA-3CFA-454A-930F-9DDF7C3D1AF2@me.com>
To: Corey Ford <cford@mozilla.com>
On Jul 12, 2013, at 9:37 AM, Corey Ford <cford@mozilla.com> wrote:

> 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).

Thanks for the write-up, Corey! That sounds like a good starting point for a spec.

[There are various whitespace issues with your text, but I assume those are copy/paste issues.]

Simon
Received on Friday, 12 July 2013 17:46:31 UTC

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