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Re: [css3-backgrounds] Example XV inconsistent with prose of section 3.6

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 13 Sep 2010 18:22:30 -0700
Message-ID: <AANLkTimAoOheHukCX=0yM2TPzsNULr=z3Kz-ZtaP9ssG@mail.gmail.com>
To: Sylvain Galineau <sylvaing@microsoft.com>
Cc: Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
On Mon, Sep 13, 2010 at 6:15 PM, Sylvain Galineau
<sylvaing@microsoft.com> wrote:
>> From: www-style-request@w3.org [mailto:www-style-request@w3.org] On
>> Behalf Of Tab Atkins Jr.
>> Sent: Monday, September 13, 2010 4:59 PM
>> To: Brian Manthos
>> Cc: www-style@w3.org
>> Subject: Re: [css3-backgrounds] Example XV inconsistent with prose of
>> section 3.6
>>
>> On Mon, Sep 13, 2010 at 4:55 PM, Brian Manthos <brianman@microsoft.com>
>> wrote:
>> > From: Tab Atkins Jr. [mailto:jackalmage@gmail.com]
>> >> On Mon, Sep 13, 2010 at 4:47 PM, Brian Manthos
>> >> <brianman@microsoft.com> wrote:
>> >>> http://dev.w3.org/csswg/css3-background/
>> >>> 3.6  The ‘background-position’ property If only one value is
>> >>> specified, the second value is assumed to be ‘center’.
>> >>>
>> >>> 3.10  The ‘background’ shorthand property p { background: 40%
>> >>> url("chess.png") / 10em gray
>> >>>        round fixed border-box; }
>> >>> is equivalent to:
>> >>> …
>> >>> background-position: 40% 50%;
>> >>> …
>> >>>
>> >>>
>> >>> I believe this is incorrect.
>> >>>
>> >>> The equivalent is
>> >>>         background-position: 40% center; or
>> >>>         background-position: 40%;
>> >>>
>> >>>
>> >>> Am I misunderstanding?
>> >>
>> >> 'center' and '50%' are equivalent in the context of a background-
>> position.
>> >
>> > For rendering yes, for OM no...
>>
>> Ah, right.  Yeah, then that example is incorrect.
>>
> Why ? This module and its examples are not about the OM so I'm not clear on why
> we can deem this example incorrect on OM grounds. But beyond that why is 50% not
> equivalent to center in the OM ?

Well, it's not specified in any significant way, but it would be
expected that saying "center" would make the current OM return
"center", and saying "50%" would make the current OM return "50%".
The Values API that Anne's been floating would differentiate between
the two as well, claiming the type of the value to be "keyword" and
"percentage" respectively.  (Like it allows you to differentiate
between "red" and "#f00".)

~TJ
Received on Tuesday, 14 September 2010 01:23:22 GMT

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