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Re: [css3-writing-modes] Keyword alternatives to "logical"

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 27 Oct 2010 18:23:20 -0700
To: Koji Ishii <kojiishi@gluesoft.co.jp>
Cc: MURAKAMI Shinyu <murakami@antenna.co.jp>, Hakon Wium Lie <howcome@opera.com>, John Daggett <jdaggett@mozilla.com>, David Hyatt <hyatt@apple.com>, "www-style@w3.org" <www-style@w3.org>, Yasuo Kida <kida@apple.com>
Message-ID: <20101028012320.GA1778@pickering.dbaron.org>
On Wednesday 2010-10-27 20:10 -0400, Koji Ishii wrote:
> > > I don't understand why 'of-block' would mean that the margins given
> > > are in before-end-after-start order rather than top-right-bottom-left.
> > 
> > When the text in a block is rotated or flipped by writing-mode or direction property,
> > "before" side is "top of block", so I thought "margin top of block 1em" can be meaningful
> > in English.
> It may be a little more understandable if you look at picture at:
> http://dev.w3.org/csswg/css3-writing-modes/#text-flow
> In the first picture, "top of block" is top side, while in the
> last picture, "top of block" is right side.

I think the working group has been clear that the terms 'top',
'right', 'bottom' and 'left' should never change their meaning based
on writing system, but instead always retain their usual meanings.

Or, to put it rather more formally, given the unit length vector ๐ž
from the reader's left eye toward the reader's right eye in the
expected reading position, the unit length vector ๐ from the point
between the user's eyes toward the center of the display, the vector
๐ฎ = ๐ž โจฏ ๐, and the vector ๐ญโฐ the projection of ๐ฎ into the plane of
the display, and the vector ๐ญ being the one of the four unit-length
vectors parallel to an edge of the rectangular display with which ๐ญโฐ
has the largest dot product, the top side of the block should be the
side of the block pointed to by ๐ญ.

Likewise, for right, given ๐ซ as the remaining one of the four
unit-length vectors parallel to an edge of the display such that
๐ซ ยท ๐ญ = 0 and ๐ซ ยท ๐ž > 0, the right side of the block is the side of
the block pointed to by ๐ซ.

And likewise for bottom using ๐› = -๐ญ and left using ๐ฅ = -๐ซ.


L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Thursday, 28 October 2010 01:24:20 UTC

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