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Re: Relatively positioned box inside an absolutely positioned box

From: Lev Solntsev <greli@mail.ru>
Date: Tue, 25 Jun 2013 15:07:14 +0400
To: "Glen Huang" <curvedmark@gmail.com>
Cc: "www-style list" <www-style@w3.org>
Message-ID: <op.wy8eicaj39dhqv@lev-pc>
Glen Huang <curvedmark@gmail.com> wrote Tue, 25 Jun 2013 08:57:25 +0400:

> I know you said below that out of flow children are exceptions. but the  
> point here is that browsers are able to calc the height of elements  
> >that depends on content height before the elements are closed, even  
> though it's very expensive like you said.
I don't think it's expensive in this case. Since they are out of the flow  
and have no impact on the document and no circular references, they can be  
just rescheduled for computing later when the height is already known.

I must state that all what I'm saying is just my thinking, based on my  
knowledge of specification, how browsers work in general, and programming  
basics. I never had a look into a real browser engine, and a real engine  
can have own implementation peculiarities.

> This explains a lot, but where do you get that conclusion? The CSS spec  
> doesn't seem to have stated that. Or did you inferred it from the  
> >definitions of height, min-height and alike properties?
In your case I think it's
> “If the height of the containing block is not specified explicitly  
> (i.e., it depends on content height), and this element is not  
> >absolutely positioned, [then] the [height] value computes to ‘auto’.”  
> coming from CSS 2.1, Section 10.5 Content height: the >'height' property
> http://www.w3.org/TR/CSS21/visudet.html#the-height-property
as Gérard Talbot stated it in his answer. Chapter “10 Visual formatting  
model details” contains all that complex topic about computing styles.
Generally, I'm basing on my experienced, read articles and discussions in  
this mailing list. There where a lot about CSS 2 couple years ago. BTW,  
CSS 2.1 specification was written with taking in account browser vendor  
considerations. Subjects that are difficult to implement, very complex or  
have lack of implementation were punted (like text-shadow) or undefined  
(like relative positioning or min/max-width on tables). That's why I'm  
telling about browser point of view.

> I can understand the rational behind the conclusion is to avoid  
> self-dependence, for a in-flow child needs to know the height of its  
> >containing block, it's very likely to change it's own height, and thus  
> in turn changes the containing block's height.
Like I said, it's a complex topic. There a lot of possibilities circular  
references, even non-obvious like appearing scrollbars in the viewport or  
element with ‘overflow: auto’.
Received on Tuesday, 25 June 2013 11:07:46 UTC

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