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Re: [css3-color] Interaction of 'opacity' and z-ordering rules

From: L. David Baron <dbaron@dbaron.org>
Date: Tue, 13 May 2008 18:22:48 -0700
To: www-style@w3.org
Message-ID: <20080514012248.GA27031@pickering.dbaron.org>

On Tuesday 2008-05-13 17:00 -0700, L. David Baron wrote:
> I propose addressing  these issues by adding the following paragraph
> to the end of section 3.2 of
> http://dev.w3.org/csswg/css3-color/#transparency :

Let me try that again:

  # Since an element with opacity less than 1 is composited from a
  # single offscreen image, content outside of it cannot be layered
  # in z-order between pieces of content inside of it.  For the same
  # reason, implementations must create a new stacking context for
  # any element with opacity less than 1.  If an element with
  # opacity less than 1 is not positioned, implementations must
  # paint the layer it creates, within its parent stacking context,
  # at the same stacking order that would be used if it were a
  # positioned element with 'z-index: 0' and 'opacity: 1'.  If an
  # element with opacity less than 1 is positioned, the 'z-index'
  # property applies as described in [[CSS21]], except that 'auto'
  # is treated as '0' since a new stacking context is always
  # created.  See <a
  # href="http://www.w3.org/TR/CSS21/visuren.html#layers">section
  # 9.9</a> and <a
  # href="http://www.w3.org/TR/CSS21/zindex.html">Appendix E</a> of
  # [[CSS21]] for more information on stacking contexts.  The rules
  # in this paragraph do not apply to SVG elements, since SVG has
  # its own <a
  # href="http://www.w3.org/TR/SVG11/render.html">rendering
  # model</a> [[SVG11]].

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Wednesday, 14 May 2008 01:23:22 GMT

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