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

[Werner LEMBERG]

> 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).

It's exactly the half of the ideographic square.

> So effectively their line breaking behavior is very different.

Maybe.  However, the most important property is to be able to start a
new line after (almost) any half-width kana.

> They are harmonized to be used along with other alphabetic
> scripts. In fact they may even not be really "half-width" but
> proportional.

Do you have an example for that?  I've *exclusively* seen fonts where
half-width kanas are really half the CJK width.

> If rendered in vertical lines, they could be either rotated (just
> like Latin letters),

Actually, I haven't seen half-width kanas ever used in vertical
context.  Does this exist?

> So IMHO, those "half-width" letters are in fact to be considered as
> another separate script, for typographic purpose.

Yes, for typographic purposes.  But typographic issues are not covered
by Unicode.  AFAIK, the existence of half-width kanas in Unicode is
purely for backwards and round-trip compatibility.


    Werner