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Re: Issue with margin-collapse-clear-012.htm and margin-collapse-clear-013.htm

From: Gérard Talbot <css21testsuite@gtalbot.org>
Date: Sat, 30 Nov 2013 19:25:46 -0500
To: Bruno Fassino <fassino@gmail.com>
Cc: Robert Hogan <robhogan@gmail.com>, Public CSS test suite mailing list <public-css-testsuite@w3.org>
Message-ID: <3b898e2b9888b2f944f32c9de1bfb3c1@gtalbot.org>
Le 2013-10-26 12:31, Bruno Fassino a écrit :
> On Thu, Oct 24, 2013 at 7:51 PM, Robert Hogan <robhogan@gmail.com> 
> wrote:
> 
>> I'm questioning the expected rendering of this part of
>> margin-collapse-clear-012.htm:
>> 
>> <div id="parent">
>>   <div id="float" style="float:left; height: 100px; width: 100px;
>> background-color:blue;"></div>
>>   <div id="self-collapsing-with-clearance" style="clear: both;
>> margin-top: 40px; margin-bottom:80px"></div>
>>   <div id="following-sibling" style="margin-bottom:140px;"></div>
>> </div>
>> 
>> The test results expect "self-collapsing-with-clearance" to receive a
>> clearance of 60px - this is a result of subtracting the margin-top
>> from the height of the float it has to clear (100px - 40px).
>> 
>> However I believe the correct clearance is 20px. I say this because
>> the margins in "self-collapsing-with-clearance" collapse together
>> giving a collapsed margin-top value of 80px (max(margin-top,
>> margin-bottom)) and it is this value that has to be used to determine
>> the clearance: 100px - 80px = 20px
>> 
> 
> 
> Hi Robert,
> 
> I believe the test is correct.
> 
> It's true that the margins of "self-collapsing-with-clearance" collapse
> together to a value of 80px, but the clearance is added:
> "to place the (top) border edge of the block even with the bottom outer
> edge of the lowest float that is to be cleared"  (from
> http://www.w3.org/TR/CSS2/visuren.html#flow-control  after the part you
> mentioned).
> 
> Now where is the "top border edge" of a self collapsing block?
> For our case the relevant part is at
> http://www.w3.org/TR/CSS2/box.html#collapsing-margins towards the end:
> "The position of the element's top border edge is the same as it would 
> have
> been if the element had a non-zero bottom border"
> 
> So the margins of our "self-collapsing-with-clearance" collapse 
> together to
> 80px and the top border edge of the box is at 40px in the middle of 
> that.
> Clearance has to be added to this position, not to the whole 80px.  So
> clearance is 60px as stated in the test, not only 20px.
> 
> Same thing for the other test margin-collapse-clear-012.htm.
> 
> I hope this is clear and correct (each time I reread these parts of the
> spec and try to apply them a non trivial case, I found this operation
> difficult).
> 
> 
> On Thu, Oct 24, 2013 at 3:11 AM, Gérard Talbot
> <css21testsuite@gtalbot.org>wrote:
>> I can see 1 comment (lines 96 to 98) in margin-collapse-clear-013.htm
> which is not right though.
> 
> Sure! We probably copied this comment from the previous test, 
> forgetting to
> adapt it.
> It should say:
> 
> (140px - 40px) :  part of #clear-left's margin-bottom exceeding
> #clear-left's margin-top
> 
> or something like that.
> 
> 
> Bruno

Bruno, Robert,

I corrected the comment and added an explanation about the vertical 
position of the top border edge of the self collapsing
element:


http://test.csswg.org/shepherd/testcase/margin-collapse-clear-013/changeset/5863/

Gérard
-- 
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CSS 2.1 Test suite RC6, March 23rd 2011
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Received on Sunday, 1 December 2013 00:26:23 UTC

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