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Re: [CSS21] Clearance paradox

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 12 Aug 2009 09:01:22 -0700
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <20090812160122.GA18096@pickering.dbaron.org>
On Wednesday 2009-05-20 08:01 -0700, fantasai wrote:
> Anton Prowse wrote on 2 Apr 2009:
>> The least disruptive solution to the problem discussed therein is to say
>> that an element can still be said to have clearance even if that
>> clearance is zero.  In other words, clearance is a property that
>> elements may possess in addition to being a quantity which is applied.
>> This makes the whole thing hold together conceptually, and required no
>> conceptual changes to the 'clear' property.  To put it another way, the
>> specification currently incorrectly equates zero clearance with no
>> clearance, yet the two concepts would be different under the solution
>> above.  Of course, this solution requires some editorial changes to the
>> text of 9.5.2 The 'clear' property
>> (http://www.w3.org/TR/CSS21/visuren.html#propdef-clear) and 8.3.1
>> Collapsing margins
>> (http://www.w3.org/TR/CSS21/box.html#collapsing-margins) where clearance
>> is sometimes regarded as solely a quantity through the implication that
>> zero clearance implies /no/ clearance.

Such changes are *far* from editorial.  If an element is considered
to have cleareance even when it would not otherwise be adjacent to
floats, then large numbers of margins that today collapse (and have
according to all prior CSS definitions) would stop collapsing, which
would be a significant break with Web-compatibility.

I don't think we can make this change.

-David

> Proposed changes:
>
> 9.5.2 Controlling flow next to floats: the 'clear' property
>
> Change
>   # Clearance is introduced as spacing above the margin-top of an element.
>   # It is used to push the element vertically (typically downward), past
>   # the float.
> to
>   | Values other than 'none' introduce clearance as spacing above the
>   | margin-top of an element. Clearance inhibits margin collapsing and
>   | is used to push the element vertically past the float.
> and shift to after value definitions.


-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Wednesday, 12 August 2009 16:01:58 GMT

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