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[csswg-drafts] Proposal: cjk-dir: new property for RTL horizontal CJK, as well as for vertical CJK together with RTL(Arabic, Persian, etc.) text (#3608)

From: 張俊芝 via GitHub <sysbot+gh@w3.org>
Date: Sat, 02 Feb 2019 10:28:22 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-405970576-1549103301-sysbot+gh@w3.org>
Zhang-Junzhi has just created a new issue for https://github.com/w3c/csswg-drafts:

== Proposal: cjk-dir: new property for RTL horizontal CJK, as well as for vertical CJK together with RTL(Arabic, Persian, etc.) text ==
In [Issue 2754](2754) I proposed a new value `horizontal-tb-rl` to `writing-mode`.

Now I would like to **bring up an improved proposal to replace the older one**:

Instead of adding a new value `horizontal-tb-rl` to `writing-mode`, it would be better to add a new property `cjk-dir`.

Let's think about vertical CJK text together with LTR text. It is reasonably rendered in a consecutiveness way, because vertical CJK characters are "by default" mapped as Top-Left/Bottom-Right in vertical mode:

![cjk-dir3](https://user-images.githubusercontent.com/37146899/52163051-7f996080-2717-11e9-9d60-6bc95dee96b7.png)

But when it comes to displaying vertical CJK together with RTL text, such as Persian, it is not as readably rendered as with LTR Latin text, because CJK and Persian text are rendered bi-directionally:

![cjk-dir1](https://user-images.githubusercontent.com/37146899/52163060-b0799580-2717-11e9-80c1-e3d018116ad0.png)

However, in vertical mode, it shouldn't have had to be in that way, bacause CJK characters can be mapped Top-Right/Bottom-Left as well as Top-Left/Bottom-Right. So here comes the new property `cjk-dir`, it changes the CJK characters' default directionality(remap them as Top-Right/Bottom-Left), without any necessary rendering change for CJK characters themselves:

![cjk-dir2](https://user-images.githubusercontent.com/37146899/52163064-c25b3880-2717-11e9-9272-527c3c008f8d.png)

The image above shows the vertical text with `cjk-dir: ltr` on the left, and shows the other one with `cjk-dir: rtl` on the right(being obviously more readable than the left bidi one).

`cjk-dir` can also as perfectly slove [Issue 2754](2754), which was about RTL CJK in horizontal mode.


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3608 using your GitHub account
Received on Saturday, 2 February 2019 10:28:24 UTC

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