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

Philippe Verdy verdy_p at wanadoo.fr
Tue Apr 28 02:47:40 CDT 2015

My feeeling is that half-width kanas behave like Latin letters and do not
even have to follow the ideographic composition square to line up with them
(unlike standard kanas). So effectively their line breaking behavior is
very different.

Those "half-width letters" are in fact similar to linear jamos (not
composed into syllabic squares) in the Korean script, and to Bopomofo
letters. And may be we could add the CJK key letters (radicals used for
example in IDS) to this list, or Yi radicals.

They are harmonized to be used along with other alphabetic scripts. In fact
they may even not be really "half-width" but proportional. They are also
used with non-ideographic punctuation (notably the ASCII punctuation) and
standard SPACE (U+0020).

If rendered in vertical lines, they could be either rotated (just like
Latin letters), or not (aligned horizontallly like letters in columns of
crosswords, but they may also have proportional height, like in
Latin/Greek/Cyrillic where it is sometimes needed for example with capital
letters with stacked accents, or when using sized spaces)

So IMHO, those "half-width" letters are in fact to be considered as another
separate script, for typographic purpose. They are "unified" with
non-halfwidth letters, only for collation with minor differences
(plain-text searching and sorting).

2015-04-28 4:20 GMT+02:00 Makoto Kato <m_kato at ga2.so-net.ne.jp>:

> 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
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