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Re: getComputedStyle results

From: Joćo Eiras <joao.eiras@gmail.com>
Date: Mon, 31 Mar 2008 02:46:32 +0100
To: "Kartikaya Gupta" <kagupta@rim.com>, "www-dom@w3.org" <www-dom@w3.org>
Message-ID: <op.t8uxvudbjz3wb9@foobar.wag54gs>

Na , Kartikaya Gupta <kagupta@rim.com> escreveu:

> The getComputedStyle return value is already well defined to be the  
> "computed" values as described in  
> http://www.w3.org/TR/CSS21/cascade.html#computed-value.

Yes, computed values are well defined, but DOM 2 StyleSheets defines  
getComputedStyle to return absolute (or used) values, not computed values.
That's the issue.

> That's what UAs are supposed to be returning. The computed results are  
> what come out of the cascade, but before the actual layout algorithm is  
> run. In some cases "auto" is the correct value to be returned, since  
> those values cannot be determined until layout time. The actual  
> representation of the value (i.e. rgb(n,n,n) vs #rrggbb) isn't  
> specified, so if you want to be safe you can use the getPropertyCSSValue  
> method on the CSSStyleDeclaration interface to retrieve a structured  
> object rather than a string.
>
> As for getOverrideStyle, that's provided so that DOM implementers can  
> override specific styles. Styles that are returned by getOverrideStyle  
> have the highest weight in the cascade and will override all other  
> styles. It's not really of much use to web developers though.
>
> Hope that helps.
>
> -----Original Message-----
> From: www-dom-request@w3.org [mailto:www-dom-request@w3.org] On Behalf  
> Of Joćo Eiras
> Sent: Sunday, March 30, 2008 9:21 PM
> To: www-dom@w3.org
> Subject: getComputedStyle results
>
>
>
> Hi!
>
> The spec for getComputedStyle says the following:
>   >
> http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSview-getComputedStyle
>   > Return Value, CSSStyleDeclaration, The computed style. The
> CSSStyleDeclaration is read-only and contains only absolute values.
>
> A broad description for absolute (or used) value can be found here
>   > http://www.w3.org/TR/CSS21/cascade.html#used-value
>
> Now, the problem is that the absolute value description is too generic,
> and currently browsers return different results for different properties,
> when calling getComputedStyle. Like:
>   - Mozilla and Safari retuns rgb(n,n,n) for colors while Opera returns
> #rrggbb (imo, Safari copied Moz just for the sake of market share)
>   - Mozilla many times retuns auto for many dimensions properties like
> height, width, top,left... while Opera returns always proper pixel
> dimensions
>   - Mozilla and Safari sometimes return keywords for quantitative
> properties like font-weight. By default getComputesTyle returns "normal"
> for these browsers, while Opera returns a numeric value (normal computes
> to 700).
>
> So, we need the spec to detail how colors, dimensions and other  
> properties
> should be represented when returned by getComputedStyle. IMO, Opera's
> implementation is more useful. Having keywords for quantitative  
> properties
> is useles, you can't do arithmetics with them.
>
> But these are use cases where we need to get the current applied cascaded
> styles, not absolute ones. How can we get this kind of information? Does
> getOverrideStyle fit this profile ?
>
> Thank you.
>
>
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Received on Monday, 31 March 2008 01:47:39 GMT

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