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Re: [CSS3] Some clarifications on background-position four values parsing.

From: Alexis Menard <alexis.menard@intel.com>
Date: Fri, 9 Nov 2012 10:41:51 -0300
Message-ID: <CAOaK9AkK+vDd4t4WJwbQ_WMTSvH1Up3KBgOC6UMLaeFi80wo5g@mail.gmail.com>
To: www-style@w3.org
On Fri, Nov 9, 2012 at 10:08 AM, Alexis Menard <alexis.menard@intel.com> wrote:
> Hi there,
>
> I was doing the implementation of background-position with four values
> and while writing the tests I found few cases where I'm not sure how
> WebKit (or any other UA should behave).
>
> Few assumptions :
>
> - The spec doesn't enforce in the case of 4 values whether the first
> pair of values is horizontal and the second vertical. So : top 30px
> right 15px is valid and produce the same result as if it was right
> 15px top 30px.
>
> - center keyword is possible as the spec doesn't explicitly say it's
> invalid value when you specify 3 or 4 values.
>
> Now here are the case I'm not sure what's the behaviour. Some of them
> could be stupid or have actually shortcuts by specifying two values
> but let's assume someone write them.
>
> - center top 20px will actually set the property to left 50% top 20px.
> This is the Opera 12.10 behaviour.
>
> - left 20px center will actually set the property to left 10px top
> 50%. This is the Opera 12.10 behaviour.
>
> - left center top 20px is treated as invalid by Opera 12.10. Could it
> be left 50% top 20px for the actual property value? Is Opera wrong?
>
> - left center top center is treated as invalid by Opera 12.10. Could
> it be left 50% top 50% or just center?
>
> - top 20px center is treated as invalid by Opera 12.10. Could it be
> left 50% top 20px for the actual property value?
>
> - right 20px top center is treated as invalid by Opera 12.10. Could it
> be right 20px top 50% for the actual property value?
>
> I'm fine matching the behaviour of Opera (though I'm not sure it's
> correct) but I'd like to understand why and maybe we should clarify a
> bit the specification on that part. I'm sure some people will play
> around with equivalent of right 20px top center.

ok

so the spec say :

<position> = [
  [ left | center | right | top | bottom | <percentage> | <length> ]
|
  [ left | center | right | <percentage> | <length> ]
  [ top | center | bottom | <percentage> | <length> ]
|
  [ center | [ left | right ] [ <percentage> | <length> ]? ] &&
  [ center | [ top | bottom ] [ <percentage> | <length> ]? ]
]

which I misread (confused || with |).

Opera is correct.

Really sorry for the noise.



>
> People have other obscure cases in mind too?
>
> Thanks.
>
> --
> Alexis Menard
>
> Intel Semiconductores do Brasil Ltda.
> Ave Dr. Chucri Zaidan, 940, Brooklin, 10 Andar
> 04583-904 São Paulo, SP
> Brazil
>
> This e-mail and any attachments may contain confidential material for
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-- 
Alexis Menard

Intel Semiconductores do Brasil Ltda.
Ave Dr. Chucri Zaidan, 940, Brooklin, 10 Andar
04583-904 São Paulo, SP
Brazil

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
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Received on Monday, 12 November 2012 07:22:14 GMT

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