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Re: [css3-background] "Margins are always transparent" missing

From: Gérard Talbot <www-style@gtalbot.org>
Date: Wed, 10 Apr 2013 16:48:17 -0400
Message-ID: <5ba8fee7ca9d2690cbfdd06061351916.squirrel@ed-sh-cp3.entirelydigital.com>
To: "Simon Sapin" <simon.sapin@exyr.org>
Cc: "W3C www-style mailing list" <www-style@w3.org>

Le Mer 10 avril 2013 16:14, Simon Sapin a écrit :
> Le 10/04/2013 21:40, "Gérard Talbot" a écrit :
>> I still do not see where this is explicitly stated. As presented,
>> background-clip defines (can set) the background painting area; but
>> nowhere does it say that background (background color and background
>> image) - by definition - of an element is never painted into its own
>> margin area.
>
> I don’t see what’s missing here. By definition, each background layer
> is
> painted in its background painting area, as defined by the
> background-clip property, and not outside of it.

Simon,

What's missing is the definition of where background (color and image) are
painted by definition and by default, where background painting starts by
definition, regardless of background-clip computed value and regardless of
background-clip definition.


> Each of the values accepted by background-clip − border-box,
> padding-box, content-box − defines an area, none of which has any
> intersection with the margins.
>
> Since there is no 'margin-box' value for background-clip, it seems very
> obvious to me that backgrounds are never painted in the margins.


Implicitly, you may/should reach such conclusion/deduction. But it is not
explicit.
This was more explicit in CSS 2.1.
It is not explicit in CSS 3 Backgrounds and Borders.
It is not explicit in CSS 3 Box model.

"
parent box's background will shine through by default because of the
initial 'transparent' value on 'background-color'.
"
CSS 2.1, section 14.2 The background
http://www.w3.org/TR/CSS21/colors.html#background

But even such statement does not fully and completely state everything.
The parent box's drawing colors (foreground) may shine through or may be
perceivable in the margin area of its child(ren).

One additional idea: use (with permission) or add a link to this image by
Jon Hicks
http://www.hicksdesign.co.uk/journal/3d-css-box-model
and/or even use (with permission) or add a link to this Flash by Douglas
Livingstone
http://www.redmelon.net/tstme/box_model/
into related CSS 3 specs.

Gérard
-- 
CSS 2.1 Test suite RC6, March 23rd 2011
http://test.csswg.org/suites/css2.1/20110323/html4/toc.html

Contributions to CSS 2.1 test suite
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Received on Wednesday, 10 April 2013 20:48:55 UTC

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