[css-ruby-1] ruby overhang control

[stantonma]

We (Kindle) have received feedback from publishers that overhanging ruby can confuse younger readers since the annotation/pronunciation is no longer directly above the base character. We'd like to give publishers the option to disable ruby overhang for certain content types like children's books.

This could also let us define the JLREQ default overhang of one ruby text character length as the default.

Proposed addition would be:

Name	ruby-overhang-limit
Value	<length>
Initial	1em

Sets the maximum allowable overhang of ruby over allowable base characters. Length is relative to the ruby text font size.

[frivoal]

The current spec leaves the limit undefined and up to the UA. Which means implementations could possibly set it to 0 to disallow all overhang, and this seem to be what Firefox does.

Interestingly, disallowing overhand altogether is the recommendation of Professor Kobayashi as a good enough solution for general use (see list item number 4 in https://w3c.github.io/jlreq/docs/simple-ruby/#placement-of-mono-ruby-0 for mono-ruby, list item number 4 in https://w3c.github.io/jlreq/docs/simple-ruby/#placement-of-group-ruby-0 for group ruby, and list item number 4 in https://w3c.github.io/jlreq/docs/simple-ruby/#placement-of-jukugo-ruby-0 for jukugo ruby).

If disallowing overhand always is not acceptable, and we do introduce a property, I would therefore suggest that the initial value be auto (i.e. up to the UA, possibly 0) or 0 rather than 1em.

[upsuper]

Overhanging control is something tricky actually. It's not just a single limit, but a bunch of rules.

For example, WebKit allows overhanging up to 1/2 (or something close) character of the ruby text regardless of surrounding characters, which is fine. Another possible rule is to overhang up to one whole ruby text, but only over certain kinds of characters (kanas & punctuations IIRC). But you should never hang a whole ruby annotation on a kanji before or after. These rules cannot really be covered by a single distance.

[frivoal]

ruby-overhang: auto | none is probably a safe minimal subset. Whether we can eventually express different kinds of non-none behavior, with or without numeric parameters, is a separate question, but unless we're comfortable banning overhand always (which I don't think we are), having the ability to opt out of overhand seems useful (as evidenced by the reqests Amazon has been getting).

[upsuper]

That sounds like a reasonable proposal.

[stantonma]

Sounds reasonable to me as well, and would cover our use cases

[macnmm]

I am surprised at the example of jukugo ruby where overhang of Kanji is allowed so as to preserve base text spacing. I would think this is an optional behavior but the default is to prevent overhang on Kanji, and only allow on kana and aki. I think having these rules as part of the minimum requirements is desirable.

[stantonma]

If we don't allow overhang within a Jukugo, then there would be no difference between if the author used a series of mono/group ruby right?

I'd prefer to leave that decision up to the UA by default (Kindle's implementation does allow it).

Though that does bring up if the property should apply to overhang within a Jukugo as well. I don't have any concern with saying it affects both cases.

[hftf]

See also #3498.

[stantonma]

Summarizing the comments above, I think we have this:

Name	ruby-overhang
Values	auto | none
Initial	auto

Controls the overhang of the ruby annotation box on adjacent text to its corresponding ruby base box.

'auto'

• The UA determines whether to overhang the ruby annotation box

'none'

• The ruby annotation box must not overhang any adjacent boxes to its corresponding ruby base box.

This way the 'none' value covers overhang for mono/group as well as overhang within a jukugo ruby.

@macnmm is the JLTF ok to move forward with this? Kindle is ready to implement.

[macnmm]

@w3c/jlreq-editors ^^ see above question to me

[murata2makoto]

I recently read the editors' manual for magnified textbooks for low-vision. First, the font size for ruby appears to be 70%. Although 50% is used for junior high school textbooks, I doubt that the use of such small ruby is due to the cost and weight of magnified textbooks. Second, ruby-overhand is not used. But space between base characters is expanded.

If you can read Japanese, the editors' manual is very interesting. Even if you cannot, please have a look at examples in this page. The first figure shows a page of a usual textbook while the second shows the same page in a magnified textbook.