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Re: [css-backgrounds] background-position-x/-y, logical positions, and initial value failure

From: MURAKAMI Shinyu <murakami@antenna.co.jp>
Date: Fri, 18 Apr 2014 13:06:32 +0900
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
Message-Id: <20140418130632.C2E4.C598BCD7@antenna.co.jp>
"Tab Atkins Jr." <jackalmage@gmail.com> wrote on 2014/04/18 10:17:27
> On Thu, Apr 17, 2014 at 5:50 PM, fantasai <fantasai.lists@inkedblade.net> wrote:
> > But with background-position, the initial values are
> >   background-position-x: left /* defined by CSS1 */;
> >   background-position-y: top /* defined by CSS1 */;
> > There is no way to express an equivalent in logical terms:
> >   background-position-inline: start;
> >   background-position-block:  start;
> > is only equivalent when writing-mode is LTR-TB. Initial values
> > don't have a cascading order, so when the writing mode is not
> > LTR-TB, what wins?
> >
> > I'd like to have background-position-x/y, but we're missing a
> > solution to make it actually work.
> I think we can resolve this by fiat.  When there's no cascade
> information dictating which property should win, we declare that the
> physical ones should win.  This only has an effect when there are no
> rules setting the property at all, in the author or UA sheets, and so
> it's purely a matter of maintaining web compat.

I agree with this. We have implemented 'background-position' with 
the initial value 0% 0% (= left top, even in any writing mode).
This means, for example, the 'background-position-block: end' will be 
the default in the vertical-rl writing mode.
In my opinion, logical directional default values are important 
for text flow, but not so for graphics and decorative things.

Shinyu Murakami
Antenna House
Received on Friday, 18 April 2014 04:07:16 UTC

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