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Re: [CSS3] background-position computed value.

From: fantasai <fantasai.lists@inkedblade.net>
Date: Wed, 28 Nov 2012 13:03:55 -0800
Message-ID: <50B67C3B.1040301@inkedblade.net>
To: www-style@w3.org
On 11/28/2012 12:16 PM, Menard, Alexis wrote:
> Hi,
>
> I’m a bit puzzled on the CSS3 computed style value for background-position.
>
> In CSS 2.1 the computed value is defined as “ for <length> the absolute value, otherwise a percentage”. It will always return
> two values, so for example “left” will return 0% 50%, “30px 40px” will return 30px, 40px. FF, Opera, and WebKit behaves like
> this, always two values are returned, no keywords.
>
> Now let’s take the definition as in CSS3. “A list, each item consisting of: two keywords representing the origin and two
> offsets from that origin, each given as an absolute length (if given a <length>), otherwise as a percentage”.
>
> So of course something like left 20px top 40px should return “left 20px top 40px”.
>
> Now my question is what about the old behavior, let say background-position was set like this : 30px 40px. Should it return
> “30px 40px” as before or should it return “left 30px top 40px” to match the definition but then break the backward
> compatibility? I believe backward compatibility should be preserved and then the specification wording is not accurate as you
> may not get two keywords and two offsets every time.
>
> As it is today Opera returns the old computed values, a list of two values and in the case of the new <position> type, the
> computed value as described by the CSS3 spec.
>
> Any thoughts?

It's a common point of confusion, but getComputedStyle() does not
return the computed style. It returns something else. And the thing
that it returns is generally serialized into its shortest form.

~fantasai
Received on Wednesday, 28 November 2012 21:04:25 GMT

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