- 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>
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 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 ๐ฎ = ๐ โจฏ ๐, and the vector ๐ญโฐ the projection of ๐ฎ into the plane of the display, and the vector ๐ญ being the one of the four unit-length vectors parallel to an edge of the rectangular display with which ๐ญโฐ has the largest dot product, the top side of the block should be the side of the block pointed to by ๐ญ. Likewise, for right, given ๐ซ as the remaining one of the four unit-length vectors parallel to an edge of the display such that ๐ซ ยท ๐ญ = 0 and ๐ซ ยท ๐ > 0, the right side of the block is the side of the block pointed to by ๐ซ. And likewise for bottom using ๐ = -๐ญ and left using ๐ฅ = -๐ซ. -David -- L. David Baron http://dbaron.org/ Mozilla Corporation http://www.mozilla.com/
Received on Thursday, 28 October 2010 01:24:20 UTC