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Re: [cssom-view] behavior of document.body.scrollTop

From: Simon Pieters <simonp@opera.com>
Date: Wed, 09 Oct 2013 11:13:47 +0200
To: www-style@w3.org, "Mike Sherov" <mike.sherov@gmail.com>
Message-ID: <op.w4ojw9bdidj3kv@simons-macbook-pro.local>
On Wed, 09 Oct 2013 04:55:14 +0200, Mike Sherov <mike.sherov@gmail.com>  
wrote:

> A recent change in Blink attempted to correct the behavior of
> document.documentElement.scrollTop and document.body.scrollTop to match  
> the
> spec and the other browsers:
>
> http://dev.w3.org/csswg/cssom-view/#dom-element-scrolltop
>
> However, it seems that the spec may inadvertently underdefine setter
> behavior on document.body.scrollTop when NOT in quirks mode. This has
> caused Blink to maintain the old, possibly incorrect behavior:
> https://codereview.chromium.org/26489005/
>
> The spec *seems* to indicate that document.body.scrollTop SHOULD NOT be a
> no-op in standards mode. If this is the intention, thank Blink is correct
> in reverting and the other browsers are wrong.
>
> However, I believe the intent is that document.body.scrollTop SHOULD be a
> no-op in standards mode (which matches other browsers. Read these steps
> carefully... nothing prevents document.body.scrollTop from getting to  
> step
> 6 in standards mode, and I believe it a spec bug, not the intention:

If the body element is scrollable, why shouldn't you scroll it?

http://software.hixie.ch/utilities/js/live-dom-viewer/saved/2558

Gecko does this, and it matches the spec, AFAICT.

Blink appears to scroll the viewport, but that's not what the spec says.

> When setting the
> scrollTop<http://dev.w3.org/csswg/cssom-view/#dom-element-scrolltop>
> attribute
> these steps must be run:
>
>    1.
>
>    If the given value is a
> ScrollOptionsVertical<http://dev.w3.org/csswg/cssom-view/#scrolloptionsvertical>
> object,
>    and the ydictionary member is not present, abort these steps.
>    2.
>
>    If the given value is a
> ScrollOptionsVertical<http://dev.w3.org/csswg/cssom-view/#scrolloptionsvertical>
> object,
>    let y be the value of the y dictionary member. Otherwise, let y be the
>    given value.
>    3.
>
>    If the element does not have any associated CSS layout
> box<http://dev.w3.org/csswg/cssom-view/#css-layout-box>,
>    the element is the root element and the
> Document<http://dom.spec.whatwg.org/#document> is
>    in quirks mode <http://dom.spec.whatwg.org/#concept-document-quirks>,  
> or
>    the element has no associated scrolling
> box<http://dev.w3.org/csswg/cssom-view/#scrolling-box>,
>    or the element has no overflow, terminate these steps.
>    4.
>
>    If the element is the root element invoke
> scroll()<http://dev.w3.org/csswg/cssom-view/#dom-window-scroll>
>     with scrollX  
> <http://dev.w3.org/csswg/cssom-view/#dom-window-scrollx>as
>    first argument and y as second, and, if the given value is a
>    ScrollOptionsVertical<http://dev.w3.org/csswg/cssom-view/#scrolloptionsvertical>
> object,
>    the given value as the third argument.
>    5.
>
>    If the element is the HTML body
> element<http://dev.w3.org/csswg/cssom-view/#the-html-body-element>,
>    the Document <http://dom.spec.whatwg.org/#document> is inquirks
> mode<http://dom.spec.whatwg.org/#concept-document-quirks>,
>    and the element does not have any vertical overflow, invoke
> scroll()<http://dev.w3.org/csswg/cssom-view/#dom-window-scroll>
>     with scrollX  
> <http://dev.w3.org/csswg/cssom-view/#dom-window-scrollx> as
>    first argument and y as second, and, if the given value is a
>    ScrollOptionsVertical<http://dev.w3.org/csswg/cssom-view/#scrolloptionsvertical>
> object,
>    the given value as the third argument.
>    6.
>
>    Scroll the  
> element<http://dev.w3.org/csswg/cssom-view/#scroll-an-element>
>     to  
> scrollLeft<http://dev.w3.org/csswg/cssom-view/#dom-element-scrollleft>
>    ,y, with the scroll behavior being the value of the behavior  
> dictionary
>    member if the given value is a
> ScrollOptionsVertical<http://dev.w3.org/csswg/cssom-view/#scrolloptionsvertical>
> object,
>    or auto otherwise.
>
> Some clarification would be greatly appreciated!
>
> Mike Sherov
> Chief Technologist
> SNAP Interactive, Inc. | Ticker: STVI
> http://snap-interactive.com | http://ayi.com


-- 
Simon Pieters
Opera Software
Received on Wednesday, 9 October 2013 09:14:19 UTC

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