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Re: Issue 158 proposed text

From: Bruno Fassino <fassino@gmail.com>
Date: Sun, 27 Jun 2010 09:50:31 +0200
Message-ID: <AANLkTimUn8CQLr9XOhe4ELFGW6X1Lwh1uEeybowj2s54@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: www-style list <www-style@w3.org>
On Wed, Jun 23, 2010 at 7:57 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> Another attempt at resolving http://wiki.csswg.org/spec/css2.1#issue-158 .
>
> For recap, the current relevant section of 9.5.2 reads as follows:
[...]
>
> I propose replacing this section with the following text:
> """
> Computing the clearance of an element on which 'clear' is set is done
> by first determining the hypothetical position of the element's top
> border edge within its parent block.  This position is determined
> after the top margin of the element with all appropriate preceding
> margins, per normal margin-collapsing rules.
>
> If this hypothetical position of the element's top border edge is
> flush with or past the relevant floats, then no clearance is applied.
> Otherwise, the top margin of the element no longer collapses with
> preceding margins, and the clearance is set to the greater of:
> * The amount necessary to place the top border edge of the block even
> with the bottom outer edge of the lowest float that is to be cleared.
> * The amount necessary to place the top border edge of the block even
> with the previously computed hypothetical position of the top border
> edge of the element.  (Informative Note: This is necessary to handle
> the case where the float moves due to the element's top margin no
> longer collapsing with previous margins.)
> """
>
> This addresses the test-case that fantasai was worried about*, and
> additionally clarifies several terms so that the definition is
> hopefully fully unambiguous now.  The additional informative note also
> makes it clear why the second clause is needed, when a naive reading
> would suggest that the second clause is unnecessary due to the
> hypothetical position already being established as being *less than*
> the float's bottom edge.


While this rewriting clarifies things, the "hypothetical position"
still relies on "preceding margins", which is I don't think is well
defined. In particular it is not clear if an adjacent top margin of
the first inflow child of the element has to be considered or not (see
http://lists.w3.org/Archives/Public/www-style/2010Jan/0509.html).



> In particular, here follows an ascii illustration of the test case she
> was worried about.  The top box has no margin, while the bottom box
> has a large top margin.  The small box is a float that comes between
> the other two boxes.
>
> Without clearing, the boxes look like this:
>
> ┏━━━━━━━━┓
> ┃        ┃
> ┗━━━━━━━━┛
>          ┬
>          │ (approx 4em)
>          │
>          │
> ┏━━━━━━━━┓
> ┃┏┓      ┃
> ┃┗┛      ┃
> ┗━━━━━━━━┛
>
> With a clear:left set on the bottom box, it *should* look like this:
>
> ┏━━━━━━━━┓
> ┃        ┃
> ┗━━━━━━━━┛
> ┏┓        ┬
> ┗┛        │ (approx 4em)
>          │
>          │
> ┏━━━━━━━━┓
> ┃        ┃
> ┃        ┃
> ┗━━━━━━━━┛
>
> Note that the the bottom box maintains its 4em separation from the top
> box.  Only the float moves, as the bottom box's top margin no longer
> collapse with the top box's (0px) bottom margin, so there's no longer
> anything pushing the float downwards.  The second clause then prevents
> the bottom box from gobbling up its own margin in an attempt to line
> up flush with the bottom of the float.


I'm probably misunderstanding something in this example, but:
If the float comes _between_ the two boxes then it is already in the
upper position (just below the first box) even in the first case with
margin collapsing, isn't it?


Regards,
Bruno

-- 
Bruno Fassino http://www.brunildo.org/test
Received on Sunday, 27 June 2010 07:51:00 GMT

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