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

From: Håkon Wium Lie <howcome@opera.com>
Date: Tue, 1 Jun 2010 16:16:47 +0200
Message-ID: <19461.5711.714916.575177@gargle.gargle.HOWL>
To: Boris Zbarsky <bzbarsky@mit.edu>
Cc: Håkon Wium Lie <howcome@opera.com>, "L. David Baron" <dbaron@dbaron.org>, MURAKAMI Shinyu <murakami@antenna.co.jp>, David Hyatt <hyatt@apple.com>, www-style list <www-style@w3.org>
Also sprach Boris Zbarsky:

 > >    - DDAs are mapped to their respective properties as soon as the
 > >      computed value of 'writing-mode' is known; thereafter DDAs --
 > >      their values and existence -- can be forgotton
 > 
 > Which just means that you have to keep track of _specified_ values for 
 > DDAs but not computed values.  Which is what Gecko and Webkit seem to do.

Yes, it seems that Gecko and Webkit both do this, otherwise this test
would not work:

  http://people.opera.com/howcome/2010/tests/log.html

However, if you need to keep the specified value, memory costs go up;
you suddenly have many more properties to keep track of.

 > >    - there is no DOM access to DDAs (I hope, the draft doesn't say)
 > 
 > Why not, if they have specified values?

Because you save memory by converting them to real properties and
forgetting about them, no?

 > > This undertanding is supported by [2]:
 > >
 > >   >  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.
 > 
 > That seems like an optimization based on pre-converting on the specified 
 > value level due to knowing what computed writing directon will be.  That 
 > optimization is, of course, not compatible with DOM access to the 
 > specified values, so I'm not sure it's a valid optimization.  Unless the 
 > specified-value behavior of these properties is _very_ weird.

Right. You could offer access to computed values of the DDAs by
tiltering them through the 'writing-mode' property. Which is somthing
scripts can do themselves, too. But access to specified values
requires memory. More memory than I think it's worth.

Cheers,

-h&kon
              Håkon Wium Lie                          CTO °þe®ª
howcome@opera.com                  http://people.opera.com/howcome
Received on Tuesday, 1 June 2010 14:17:46 GMT

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