From: Grant, Melinda (melinda.grant@hp.com)
Date: Wed Sep 20 2006 - 16:48:59 EDT
From HP's perspective (and I think we're not alone), the CSS
specification is difficult to interpret with respect to how margins,
borders, padding, and backgrounds work when applied to the <body> and
<html> elements. Recently we have learned that the CSS3 Paged Media
module is not clear on how the same properties used within an @page
context should interact with the html properties.
I'd like to share my new-and-improved understanding based on discussions
within the CSS WG: ;-)
* First, there are html attributes and there are css properties.
In html, the body element has a bgcolor attribute, but the html element
does not. For XHTML documents, the UA (printer) must convert the body
bgcolor attribute into an equivalent printer style rule:
So <body bgcolor="red"> gets converted into the printer
stylesheet rule: body {background-color: red}. (This gets a bit more
complicated for HTML documents, but we don't need to go there.) This
printer stylesheet rule will be overridden by an author stylesheet rule,
should one exist. See
http://www.w3.org/Style/Group/css2-src/cascade.html#q13.
* The body element is no different when it comes to CSS styling
from any other element. Backgrounds, margins etc behave just as they do
for a div, for example.
* The html element is the root element. It can also be selected
with ':root'. It is special, in that a background is applied to the
margins as well as the content area. This is because it 'paints the
canvas', which is infinite. The only way in XHTML to put a background
in the html margin area and/or the body margin area is to use a
background on the html element. (See
http://www.w3.org/TR/CSS21/colors.html#q2.)
* The attached file, 'margin-both.xhtml' when opened with Firefox,
provides an example of how html and body edgings should be rendered.
There are still some open questions about how @page properties work. I
am hoping to publish a new version within the next week or so that will
resolve questions such as the following: [My proposed answers are in
brackets.]
* Is a font property set within an @page rule applied to the page
content area (unless overridden by properties set on elements rendered
on the page), or just to the contents of the page margin boxes?
[Proposed Answer: Just to the margin boxes.]
* Do the html and page margins collapse? [no]
* Are html and body borders closed at the bottom of each page, or
just at the end of the document? [Just at the end of the document]
* Does a background property set within an @page rule get applied
to the page margins? [Yes] To the page area unless obscured by html,
body, or other backgrounds? [????, under discussion]
* On the last page of a document, do the html and body properties
terminate immediately after the last content, or at the bottom of the
page (e.g., do the html and body margins get drawn right below the last
paragraph, or at the bottom of the page? [Immediately after content.]
* Similarly, on the last page, do the page bg, border, etc. extend
to the bottom of the page, or terminate after the last content? [bottom
of the page]
* Others?
Best regards,
Melinda
_____
HP - Melinda Grant
Connectivity Standards
Consumer Printing and Imaging
+1 (541) 582-3681
melinda.grant@hp.com
_____
attached mail follows:
Hello Melinda,
> So is there any difference in XHTML between setting attributes on the
> body versus the html elements?
Do you mean attributes or properties?
The <html> element doesn't have a bgcolor attribute, only <body> does.
And in XHTML1, the bgcolor attribute is still supposed to work the same
way as in HTML. (But CSS says that the way it works is subtly
different: In HTML documents, bgcolor="red" is equivalent to 'body
{background-color: red}' in the user style sheet, except that it has
specificity=0. In XHTML documents, it is up to the UA to analyze the
document and construct an appropriate UA style sheet, e.g., with 'html
{background-color: red}'. See section 6.4.4:
http://www.w3.org/Style/Group/css2-src/cascade.html#q13)
As for CSS properties, there is absolutely nothing special about the
<body> element in XHTML. Setting 'body {background: red}' is no
different from 'div {background: red}', i.e., only the box of the body
itself is red.
The <html> element is the root element, so it is still special. And thus
the only way in XHTML to set the background of the canvas is with 'html
{background:...}'
That is, unless...
>
> (I'm still trying to figure out how body and html attributes should
> relate to @page attributes...)
... if we allow a 'background' property inside '@page', it presumably
causes a background to be rendered behind the background of the <html>
element, if any.
Bert
-- Bert Bos ( W 3 C ) http://www.w3.org/ http://www.w3.org/people/bos W3C/ERCIM bert@w3.org 2004 Rt des Lucioles / BP 93 +33 (0)4 92 38 76 92 06902 Sophia Antipolis Cedex, France
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