Bobby Jack wrote: > --- On Thu, 7/16/09, Alan Gresley <[email protected]> wrote: > >> Bobby Jack wrote: > >>> ... and an appropriate z-index :) >>> >> None is required for position: fixed. You're positioning, >> not layering (altering the paint order). > > Not if there's a relatively-positioned element on the page, in my experience: > > http://www.fiveminuteargument.com/fixed-position-z-index > > Is this a bug or expected behaviour? > > - Bobby
Hello Bobby, This is indeed expected. You are partly correct and thank you for catching me out. I never considered that the original poster (Ellen) had anything else positioned. The behavior which you have linked to is demo'd here. <http://css-class.com/test/css/visformatting/layers/pos-ab-and-pos-rel-layer1.htm> By changing the source order of the HTML alone will paint the flow of elements differently. <http://css-class.com/test/css/visformatting/layers/pos-ab-and-pos-rel-layer2.htm> Source ordering (visually layering / painting) can be achieved without any absolute positioning or z-index. <http://css-class.com/test/css/shadows/source-ordered-box-shadow.htm> Absolute or fixed positioning establishes a new 'Block Formating Context' [1]. Relative positioning establishes a 'Containing Block' and in some cases a new 'Block Formating Context' [2] [3]. None of this changes the painting order (layer) which is painted by order of the flow. Z-index creates a new 'Stacking Context' [4]. You are confusing this with the natural painting order generated by elements in the normal flow. 1. <http://www.w3.org/TR/CSS21/visuren.html#block-formatting> 2. <http://www.w3.org/TR/CSS21/visuren.html#containing-block> 3. <http://www.w3.org/TR/CSS21/visuren.html#relative-positioning> 4. <http://www.w3.org/TR/CSS21/visuren.html#layers> BTW, I, others on this list and those on the CSS working group list tackled such terms as 'painting order', 'stacking order', 'stacking context' and 'block formatting context' in 2007 (I'm still somewhat confused). Ingo Chao seemed to have visualized this stacking / painting dilemma quite well and I guess what is in the spec regarding all this is just left as it is. Rewriting the specs to conform to how browsers handle this stacking / painting is a challenge that none have ventured near. Enough said. I will leave this to some else to explain better. ;-) -- Alan http://css-class.com/ Armies Cannot Stop An Idea Whose Time Has Come. - Victor Hugo ______________________________________________________________________ css-discuss [[email protected]] http://www.css-discuss.org/mailman/listinfo/css-d List wiki/FAQ -- http://css-discuss.incutio.com/ List policies -- http://css-discuss.org/policies.html Supported by evolt.org -- http://www.evolt.org/help_support_evolt/
