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[css3-page] Each page-margin box establishes a stacking context

From: Simon Sapin <simon.sapin@exyr.org>
Date: Mon, 04 Mar 2013 11:23:33 +0100
Message-ID: <51347625.1000003@exyr.org>
To: www-style list <www-style@w3.org>

I plan to rewrite §4.1. "Page Backgrounds and Painting Order" it terms 
of stacking contexts (as in Appendix E of CSS 2.1.)

This is mostly clarification, but there is one normative change: each 
page-margin box should establish a stacking context. This change does 
not make a difference with only CSS21 + css3-page, but might eg. if we 
allow regions (with positioned children) to flow into page-margin boxes.


Here is a draft of what I want to put in §4.1. Comments welcome:


The root stacking context paints, in order:

1. The page background
2. Its "children" in z-index order (most negative first), then (for 
equal z-index values) default order.

The root stacking context’s children are, in default order:

1. The "page contents" (this is a new concept, if you have name ideas …)
2. The page-margin boxes, in clockwise order starting with @top-left-corner

The z-index property always applies to page-margin boxes; they each 
establish a stacking context.

The "page contents" has a z-index value of 0 (which can not be changed.) 
It paints, in order:

1. The document’s canvas background
2. The page border
3. The document contents (ie. the root element)


Maybe this would be easier to explain if we had two different boxes 
instead of just one page box: one "root" box that has the background 
from @page, and one "content" box that has the document canvas’s 
background (propagated from the root element) and the border from @page.

Boxes generated by the root element are children of the "content" box. 
The "content" box and page-margin boxes are children of the "root" box.

The "content" box is closest to the current concept of "page box". The 
"root" name is not great: although it is really the root, it’s very 
different from the root element.

Naming ideas?

Simon Sapin
Received on Monday, 4 March 2013 10:23:57 UTC

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