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Re: [css3-background] background-clip-009.html has 1 issue

From: Gérard Talbot <css21testsuite@gtalbot.org>
Date: Mon, 13 May 2013 18:56:40 -0400
Message-ID: <1f1a3a0352e054211ff06cae3ebfc4e0.squirrel@ed-sh-cp3.entirelydigital.com>
To: "Julien Chaffraix" <jchaffraix@webkit.org>
Cc: "Public CSS test suite mailing list" <public-css-testsuite@w3.org>

Le Dim 5 mai 2013 21:18, Julien Chaffraix a écrit :
> Hi Gérard,
>
>> http://test.csswg.org/source/contributors/google/submitted/background-clip-009.html
>>
>> There is still an issue with that test.
>>
>> You added a margin-bottom and wrote
>> "
>> Added a margin-bottom to this test as it doesn't change the output but
>> make it fail if the browser clips at the margin box.
>> "
>> http://lists.w3.org/Archives/Public/public-css-testsuite/2013Feb/0011.html
>>
>> but the thing is the background (background-color and/or
>> background-image) of an element never paints its own margin area (with
>> only the root element as the sole exception to this). Your comment
>> suggests that the margin area would be painted with black color (the
>> background-color of the element) if the clipping would not be executed
>> or would be wrongly executed. But the margin area should not be
>> painted
>> by the background-color to begin with.
>
> That wasn't the intent of my reply actually. I expect the browser to
> clip at the border box. The extra margin was designed to catch the
> case where the browser actually paints the margin box with the
> background color.

What if it would have painted the margin box and then clip at the border
box? Then we would not know that the background painting implementation
is wrong.

We have at least one test checking, verifying that background-color does
not (never!) paint the margin area of an element:

[RC6]
http://test.csswg.org/suites/css2.1/20110323/html4/margin-backgrounds-001.htm

[nightly-build]
http://test.csswg.org/suites/css2.1/nightly-unstable/html4/margin-backgrounds-001.htm

... albeit the text assert of those tests seems awkward and perfectible
to me...


> In retrospect it's probably not that much of an
> issue but I thought it was nice to have.
>
>> So, I believe we should remove
>>
>> line 23:     margin-bottom: 50px;
>>     /*
>>     Added a margin-bottom to this test as it doesn't change
>>     the output but make it fail if the browser clips at the
>>     margin box. Julien
>> line 27: */
>
> I removed these lines as they seem to have confused you

They have confused me. In my mind, in CSS 2.1, background painting is
one distinct, separate thing and then there is background clipping
(cisaillement, rogner, découper) which is another distinct, separate
thing. CSS3 seems to be merging both things together under one single
property: background-clip.

Maybe (really not sure of this as it would decisively affect all of
margin collapsing spec) CSS3 background-clip should have been split into
2 other properties: background-painting and background-clip ..

> and didn't add
> much to the test.
>
> Thanks,
> Julien

The test
http://test.csswg.org/source/contributors/google/submitted/background-clip-009.html
is fine, correct and adequate; it was also before ... only that comment
was arisen a doubt in understanding.

Gérard
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Received on Monday, 13 May 2013 22:57:26 UTC

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