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Re: [css3-background] background-position computed value

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 7 Nov 2011 14:55:09 -0800
Message-ID: <CAAWBYDCNYgt3=xsjUUT6PP75PP2Dyjz0wSdnC_RmZY6Yf_5NaA@mail.gmail.com>
To: Brian Manthos <brianman@microsoft.com>
Cc: "www-style@w3.org" <www-style@w3.org>
On Mon, Nov 7, 2011 at 2:44 PM, Brian Manthos <brianman@microsoft.com> wrote:
> For 5 and 6…
>
> http://www.w3.org/TR/css3-background/#background-position
>
> “If only one value is specified, the second value is assumed to be
> ‘center’.”
>
> http://dev.w3.org/csswg/cssom/#css-values
>
> “Where CSS component values of the value can be omitted without changing the
> meaning of the value (e.g. initial values in shorthand properties), omit
> them. If this would remove all the values, then include the first allowed
> value.”
>
> “E.g. margin: 20px 20px becomes margin: 20px.”
>
>
> Thus…
>
> Minimization rule: “<length> center” => “<length>”
>
>
>> “The B renditions of #8 and #10 are clearly wrong, as they go against the
>> explicit text of the computed value line.”
>
> I presume you are referring to the 2nd sentence.
>
> That sentence is in direct conflict with the “omission” rule that CSSOM
> describes.  This presents an inconsistency relative to IE9 behavior which I
> find troubling for back-compat and other reasons.  Setting that aside for a
> moment….
>
> The second sentence of computed value reads:
>
> If three or four values are specified, two pairs of a keyword plus a length
> or percentage.
>
> Does that mean that…
>                 center top 5px
> computes to
>                 left 50% top 5px
> rather than
>                 50% 5px (minimized)
> or
>                 center top 5px (conceptually aligned with the specified
> value)
> ?

Ah, I see what you're referring to.  The B&B text is in conflict with
the suggestion for serialization in CSSOM.  You should have mentioned
that in the OP.

In that case, I'll defer to Elika and Brad.

~TJ
Received on Monday, 7 November 2011 22:56:09 GMT

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