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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: Thu, 03 Jun 2010 12:38:09 +0900
To: Hakon Wium Lie <howcome@opera.com>
Cc: "L. David Baron" <dbaron@dbaron.org>, Boris Zbarsky <bzbarsky@MIT.EDU>, David Hyatt <hyatt@apple.com>, www-style list <www-style@w3.org>
Message-Id: <20100603123809.61F2.C598BCD7@antenna.co.jp>
Håkon Wium Lie <howcome@opera.com> wrote on 2010/06/03 5:22:09
> Also sprach MURAKAMI Shinyu:
> 
>  > >  > For UAs supporting only horizontal writing, *-before, *-after,
>  > >  > logical-width and logical-height are simply aliases of *-top, *-bottom,
>  > >  > width and height respectively. No costs needed.
>  > > 
>  > > From this, however, it is unclear if the properties turn into "real
>  > > properties" when/if vertical writing is supported.
>  > 
>  > The *-before, etc. will be pure aliases until vertical writing 
>  > is supported, and turn into DDAs when vertical writing is supported.
> 
> I don't understand. What is the difference between "pure aliases" and
> DDAs (direction dependent alias)? To me, these mean the same thing.
> That is, an "alias" is a name that can be used in style sheets (and
> perhaps also in the DOM) but there is no real property or memory
> structure underneath.

Sorry, my wording "*-before, etc." was ambiguous, it should be
"*-before, *-after, *logical-width and *logical-height"
(no *-start and *-end), and "pure aliases" might not be proper term,
What I intended to mean is: Horizontal writing only UAs can convert
these aliases to "real" properties independent of direction (ltr or rtl),
possibly, at parse time.

> 
> For example, 'margin-start: 10px' is an alias that is resolved when
> the computed value of 'writing-mode' has been determined;
> 'margin-start' is then resolved into 'margin-left: 10px', 'margin-top:
> 10px', or 'margin-right: 10px' (as you show in [1]).
> 
> Likewise, when the value of 'margin-start' is queried through the DOM,
> 'writing-mode' will be consulted to determine which of 'margin-left',
> 'margin-top', 'margin-right' that should be consulted to determine the
> value. (Or, alternatively, one could leave it to an external
> script/library to do this job.)
> 
> In this model, no new storage necessary for the alisases. 
> 
> In paged media, there is also a requirement to set values on the
> inside and outside of pages. For example:
> 
>    margin-outside: -30px
> 
> An aliasing mechainism could be the right approach.

I agree.

> 
> [1] http://lists.w3.org/Archives/Public/www-style/2010Apr/0278.html

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村上 真雄 (MURAKAMI Shinyu)
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Received on Thursday, 3 June 2010 03:38:53 GMT

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