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

From: Brad Kemper <brad.kemper@gmail.com>
Date: Tue, 8 Nov 2011 08:21:05 -0800
Message-Id: <DF24751A-AD70-452A-844A-DBCB9A12DE97@gmail.com>
Cc: Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
To: "Tab Atkins Jr." <jackalmage@gmail.com>

On Nov 7, 2011, at 2:55 PM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:

> 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.

I wasn't as involved in this part of the spec. I'll defer to Elika for now. 
Received on Tuesday, 8 November 2011 16:21:44 GMT

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