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Re: [CSS3-color] Errata

From: Chris Lilley <chris@w3.org>
Date: Tue, 17 Jul 2012 15:35:15 +0200
Message-ID: <573671298.20120717153515@w3.org>
To: "Anton Prowse" <prowse@moonhenge.net>
CC: www-style@w3.org
On Sunday, April 29, 2012, 9:34:50 PM, Anton wrote:

AP> Really sorry - I thought I'd sent a reply to this whilst at the Paris F2F
AP> but I don't think I actually did :-(.

>> Comment 3

>> Your proposed wording isn't quite sufficient because "treated as
>> though it has the index: 0" also has an effect on the painting level
>> of descendents.

>> Instead, we suggest to address your comment by changing

>> "except that ?auto? is treated as ?0?"

>> to

>> "except that a computed value of 'auto' behaves as if its z-index
>> were zero"

>> to make it clear that it doesn't change the computed value.

AP> I don't think that makes much grammatical sense, but I'm happy with the
AP> approach; it's follows the same lines as the updated suggestion that I
AP> made in [1] in response to comments.

AP> The heart of the issue is that it's not entirely clear what "behaves"
AP> means!  Is it obvious that you intend that the element takes
AP> responsibility for painting its positioned descendents (ie that
AP> responsibility doesn't bubble up to the nearest ancestor positioned
AP> element with integer z-index), but I wish it were more explicit that
AP> the used value doesn't become '0'.

AP> Here's another possibility:

AP>   | If an element with opacity less than 1 is not positioned
AP>   | then it is painted on the same layer, within its parent stacking
AP>   | context, as positioned elements with stack level 0. If an element
AP>   | with opacity less than 1 is positioned, the ?z-index? property
AP>   | applies as described in [CSS21], except that if the used value
AP>   | is 'auto' then the element behaves exactly as if it were '0'.

AP> [Note that I prefer my first sentence over the one that's in the spec,
AP> where a bit of a muddle occurs with "paint the layer" and "at the same
AP> stacking order".  My sentence precisely matches what's now CSS21
AP> terminology.]

Yes, its better to match the CSS 2.1 teminology.

AP> This addresses my concern about used value, and it's implicit that a
AP> computed value of 'auto' may still result, since that's the only way of
AP> ending up with a used value of 'auto'.

AP> In fact, would it not be much simpler to force the used value to '0' in
AP> the case that the computed value is 'auto'?  There wouldn't need to be
AP> any hand-waving at all then!

That seems like a bigger change, and not necessarily compatible with existing implementations. So I would like to propose that we accept your proposed 'another possibility' wording.

Please confirm that it is acceptable, so I can update the errata.

AP> [1] http://lists.w3.org/Archives/Public/www-style/2011Jul/0116.html

AP> Apologies again for the delay in responding.

AP> Cheers,
AP> Anton Prowse
AP> http://dev.moonhenge.net

 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups
Received on Tuesday, 17 July 2012 13:36:02 UTC

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