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Re: [css3-text-layout] New editor's draft - margin-before/after/start/end etc.

From: MURAKAMI Shinyu <murakami@antenna.co.jp>
Date: Mon, 07 Jun 2010 15:34:13 +0900
To: John Daggett <jdaggett@mozilla.com>
Cc: Boris Zbarsky <bzbarsky@mit.edu>, www-style list <www-style@w3.org>, Hakon Wium Lie <howcome@opera.com>
Message-Id: <20100607153413.2D6B.C598BCD7@antenna.co.jp>
John Daggett <jdaggett@mozilla.com> wrote on 2010/06/07 11:31:56
> Shinyu Murakami wrote:
> > I am still thinking that DDAs is a good idea and Mozilla and
> > WebKit's *-start/end implementations seem good enough. But I also
> > noted a smart proposal that fantasai wrote. See:
> > http://lists.w3.org/Archives/Public/www-style/2006Jun/0084.html
> > 
> > In this proposal, logical properties (*-before/after/smart/end) are
> > not aliases of physical properties (*-top/bottom/left/right) and
> > each property cascades and receives its specified value
> > independently and the priority between logical and physical is
> > defined by the direction-model property. In this model, it can avoid
> > "unhealthy inter-dependency between properties".
> Murakami-san, other than the fact that creating new properties
> provides a way of specifying style rules that only apply to user
> agents that support vertical text, what are the advantages of
> supporting logical properties?  I'm still unclear what the advantages
> are to this proposal beyond the fallback handling.
> John Daggett

The fallback handling is very important. We want to access to the 
documents (web or ebooks) styled as vertical writing even when we 
cannot use UAs that support vertical writing.

UAs that supprt vertical writing must suport logical properties.
The advantages of logical properties for such UAs are obvious.
They can switch writing modes (horizontal/vertical) by user preference.
It's easy to write stylesheets suited for both writing modes
using only logical properties.

UAs that support only horizontal writing need not (but should)
support logical properties.
Horizontal writing only UAs without logical properties
ignore styles using logical properties and the results will be 
poor but can be read with default HTML styles.

The advantages of supporting logical properties for horizontal
writing only UAs are:
- good results with stylesheets using logical properties
- good for RTL (margin-start/end)

To decrease implementation costs for such UAs (i.e., the block-flow
is always tb), the *-before and the *-after can be simply aliases of
*-top and *-bottom.

Best regards,

ζ‘δΈŠ ηœŸι›„ (MURAKAMI Shinyu)
Antenna House Formatter:
Received on Monday, 7 June 2010 06:34:55 UTC

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