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

From: John Daggett <jdaggett@mozilla.com>
Date: Mon, 7 Jun 2010 18:44:30 -0700 (PDT)
To: Håkon Wium Lie <howcome@opera.com>
Cc: MURAKAMI Shinyu <murakami@antenna.co.jp>, Boris Zbarsky <bzbarsky@mit.edu>, www-style list <www-style@w3.org>, "Tab Atkins Jr." <jackalmage@gmail.com>
Message-ID: <291043613.381182.1275961470950.JavaMail.root@cm-mail03.mozilla.org>

Håkon Wium Lie wrote:

> Brief analysis
> All proposals have the potenial to solve the problem at hand: to
> change certain property values when the writing-mode changes and to
> provide graceful fallback values when a UA that does not support
> vertical writing shows the document.

I would add that I think the discussion of logical vs. physical
properties is a bit of a distraction from the larger subject of how to
render vertical text correctly.  Logical properties are not *required*
to render vertical text, they simply make it easier to do certain
operations in a subset of use cases.  (I'm not discounting fallback,
but all new CSS features need to have some form of fallback behavior
for older UAs, writing-mode included).

As for required changes, at the page level there are issues of how to
deal with flow on the page, given the way scrolling works, that affect
usability much more profoundly. Behavior for properties like
'text-align' and pseudo-elements like :first-line, :first-letter needs
to be defined for the vertical text case. The CSS3 Text spec adds
'start' and 'end' values for 'text-align', this is *required* in my
mind because without it an author has no way to indicate that a given
line is bottom-aligned.  Similarly 'float' and 'clear' need to be
rethought (oh joy!).  

There are also issues deal with automatic transforms of
full-width/half-width forms which have separate codepoints; in various
cases numerals in horizontal text are rendered with half-width glyphs
but full-width glyphs are used in vertical text. Likewise, where
full-width forms are used for Latin letter in vertical text (yes,
Japanese encodings have separate codepoints for these) might be
rendered with proportional glyphs in the horizontal case. Plus
additional properties will be needed to support third-width and
quarter-width numerals, unique to vertical text.

Right now, Murakami-san is adding in features to the CSS3 Text Layout
and CSS3 Text specs but I think it might be useful to begin by trying
to summarize all of the possible changes required to support vertical
text in a single document and try and tackle the tough issues like
page flow first.


John Daggett
Received on Tuesday, 8 June 2010 01:45:36 UTC

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