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Re: [css3-page][css3-mediaqueries] Changing element styles on page breaks

From: Simon Sapin <simon.sapin@kozea.fr>
Date: Tue, 21 Feb 2012 10:02:26 +0100
Message-ID: <4F435DA2.2010004@kozea.fr>
To: Brad Kemper <brad.kemper@gmail.com>
CC: "www-style@w3.org" <www-style@w3.org>
Le 21/02/2012 09:00, Brad Kemper a écrit :
>> The semantics would be similar to regions, but there is a syntax
>> problem to disambiguate @page properties and type selectors.
>>>
>>> This is a big feature, and I wouldn’t want it to delay what is
>>> already in css3-page (especially margin boxes.) So how about this
>>> keeping full selectors for level 4?
>
> I don't see how it could be bolted on later without at least making
> allowances for it now. I don't think you could have 'a:link' (an
> element and a pseudo-class) in the same place where you could have
> 'color:green' (a property and value). I think the way to disambiguate
> would be to not have properties directly within @page, but rather
> have a selector to set the page box. I think :root could work, but if
> that is problematic, then maybe just ':page'.

Margin boxes were added just fine in the middle of @page. We can add 
anything at any time, as long as it does not start with an IDENT token 
(that would be a property name) or one of the 16 at-keywords for margin 
boxes.

Of course selectors can start with an IDENT so some kind of marker would 
be needed. But that can happen at any time.


> Also, I share Håkon's feeling that regions should not proceed too far
> without giving more thought to  how they can be used without
> requiring markup for each region box (ie, I'd say generate
> pseudo-elements that could be regions instead). Similarly, I think
> regions, pages, page masters, overflow:paged, and columns all need to
> be considered together, in terms of how they can and should affect
> each other, and how consistent they are, or could/should be, at
> solving the same sort of problems. It doesn't seem right for regions
> to be fast tracked possibly ahead of pages with the ability to style
> individual region content differently without giving a similar
> ability to pages. There is certainly use cases for that power to be
> in pages. In fact, the purpose of regions is to be able to do
> magazine-like layouts. Magazine layouts are very much layouts of
> multiple pages. How can we consider linking regions without
> considering how to link them from one page to the next with different
> page designs? That should really be something that css3-page is ready
> for. I'd rather that happen now than later.

I understand that these should be considered together but I don’t know 
how stable/ready the whole thing.

The current css3-page on the other hand adds margin boxes and page 
counters. These have been a WD for a long time and have many (at least 
partial) implementations. Here are a few:

http://weasyprint.org/#sample-output (this one is mine)
http://www.princexml.com/doc/5.1/page-headers-footers/
http://www.tufat.com/docs/html2ps/compatibility.css.3.html
http://www.antennahouse.com/CSSInfo/css_reference.html#css-property-conf-rule
http://www.realobjects.com/products/pdfreactor/demos-docs/sample-documents/page-layout-samples/
http://flyingsaucerproject.github.com/flyingsaucer/r8/guide/users-guide-R8.html#xil_40
http://blog.tallcomponents.com/2011/03/css3-page-counter.html

I’m sure more careful googling can turn up more. Though not remotely as 
much as web browsers and not in the same contexts, these implementations 
*are* in use. Almost all of them have unprefixed WD features.

The spec needs polish in corner cases (and probably a new algorithm for 
Margin Boxes Variable Dimension, but that’s another story) but I think 
it is relatively stable.


> Adding selectors inside @page is not that much more to consider. It
> should be no worse than @region, or of selecting descendants of
> :first-line.

Choosing a marker to disambiguate the syntax can be pretty quick, but 
spec’ing precisely how the cascade and layout work is another story. But 
again I don’t know stable ready it is in the Regions spec.

I think that selectors3 do not allow selecting descendants of 
:first-line (Pseudo-elements are only allowed at the end of a selector.) 
Is that in selectors4?


> My @slot goes further, but it is not much more than what
> we have with ::before and ::after, or with margin boxes, except to
> have an arbitrary number of them per paged page, and let them use
> 'flow-from'.

This sounds interesting, but please let margin boxes progress without 
attaching new features to the same spec. Do that in level 4 or in 
another module like GCPM does.

Regards,
-- 
Simon Sapin
Received on Tuesday, 21 February 2012 09:03:01 GMT

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