[css-text-3] Segment Break Transformation Rules for East Asian Width property of A

[hax]

https://drafts.csswg.org/css-text-3/#line-break-transform

Otherwise, if the East Asian Width property [UAX11] of both the character before and after the line feed is F, W, or H (not A), and neither side is Hangul, then the segment break is removed.

As this rule, common use cases of quotation marks in Chinese

简体中文的
“引号”
两边不应该有空格。

will have unexpected spaces, because quotation marks are A.

Ideally, we should consider the language information of the context. If the context is East Asian language, A should be treat as W. Even in the unknown language context, if any side of the line feed is A and other side is F, W or H, the segment break should also be removed.

[fantasai]

My concerns here are:

• Removing spaces where they currently aren't removed can break existing pages.
• The proposed behavior is more complex to understand and more complex to implement for what is a fairly low-level operation.

I'm happy to make the change if i18n recommends it and implementors agree, but I am hesitant to do so for these reasons.

[hax]

@fantasai Current segment break rule in the draft already change the traditional behavior, and up to now no browser implement it.

Do you mean you just want to drop the rule totally?

And I don't think my proposal is much complex than current.

Current rule:
if the East Asian Width property [UAX11] of both the character before and after the line feed is F, W, or H (not A)

My proposal:
if the East Asian Width property [UAX11] of both the character before and after the line feed is F, W, H, or A, except both is A.

[astearns]

@r12a waiting on i18n feedback before we get this on the CSSWG agenda again

[fantasai]

Just to clarify, the proposal is that if lang=zh|ja|yi then A->W otherwise A->N for the purpose of line-break transformations? I think that should probably be okay. I would be against making A->W the general case.

[hax]

@fantasai In fact there are two proposals:

1. If the context is East Asian language, A should be treat as W.
2. If context is not available (or if proposal 1 is not accepted), modify current Segment Break Transformation Rules for A:
   If one side of line break is A and other side is F/W/H (which means it's very likely in east asian context), then treat A as W.

[upsuper]

I think the motivation is reasonable, and some A should be treated as W in CJ context, especially quotations in Chinese. But I am concerned about A+A case, especially given that there are lots of letters in A.

The safest thing to do is probably this: if the context is Chinese or Japanese, and one side of line break is a punctuation in A, and the other side is F/W/H, then the segment break is removed.