Why doesn't Ideographic (ID) in UAX#14 have half-width katakana?

[Makoto Kato]

Hi, Suzuki-san.  Thank you for reply.

> At present, I have no objection to add halfwidth katakana
> to ideographic-class in UAX#14, but I'm unfamiliar with the
> (negative) impact caused by the lack of halfwidth katakana
> in it. Could you tell me if you know anything?

Since half-width katakana isn't ID, it isn't break line like
full-wdith katakana.

This is a sample for line break of half-width katakana.  (There is
good sample by web browser implementation)
http://mxr.mozilla.org/mozilla-central/source/layout/reftests/line-breaking/ja-3.html

Firefox and IE11 define half-width katakana as ID.  The line break of
half-width katakana is same as full-width katakana.
Chrome doesn't define it as ID.  Half-width katakana isn't line break
per character.

Although I read JIS X 4051, it doesn't define that half-width katakana
and full-width katakana are differently.


> I guess, the inclusion or exclusion in other classes, like,
> AI, AL, CJ, JL, JV, JT, SA might be quite important to realize
> the appropriate line breaking, but the inclusion or exclusion
> in ID-class does not seem to be important. If the inclusion
> in ID-class is important, more characters (e.g. Bopomofo)
> should be considered for full coverage. How do you think of?

My discussion is why half-width katanaka character isn't same class of
full-width katakana character.  In this case, half-width katakana
originally defines as AL at current spec.  So when moving to ID, break
rule is strongly changed. (non-break -> break before or after).


-- Makoto

On Tue, Apr 28, 2015 at 12:14 PM, suzuki toshiya
<mpsuzuki at hiroshima-u.ac.jp> wrote:
> Kato-san,
>
> At present, I have no objection to add halfwidth katakana
> to ideographic-class in UAX#14, but I'm unfamiliar with the
> (negative) impact caused by the lack of halfwidth katakana
> in it. Could you tell me if you know anything?
>
> I guess, the inclusion or exclusion in other classes, like,
> AI, AL, CJ, JL, JV, JT, SA might be quite important to realize
> the appropriate line breaking, but the inclusion or exclusion
> in ID-class does not seem to be important. If the inclusion
> in ID-class is important, more characters (e.g. Bopomofo)
> should be considered for full coverage. How do you think of?
>
> Regards,
> mpsuzuki
>
> Makoto Kato wrote:
>> Hi.
>>
>> http://www.unicode.org/reports/tr14/proposed.html#ID defines Ideographic
>> (ID).  Although full-width katakana is included in ID, half-width
>> katakana (U+FF66 and U+FF71-U+FF9D) isn't.  Why?
>>
>> Also, Conditional Japanese Starter (CJ,
>> http://www.unicode.org/reports/tr14/proposed.html#CJ) considers
>> half-width variants such as half-width katakana letter small a.
>>
>>
>> -- Makoto