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

Ken Whistler kenwhistler at att.net
Fri May 1 11:48:11 CDT 2015


On 5/1/2015 8:25 AM, suzuki toshiya wrote:
> Excuse me, there is any discussion record how UAX#14 class for
> halfwidth-katakana in 15 years ago? If there is such, I want to
> see a sample text (of halfwidth-katakana) and expected layout
> result for it.

The *founding* document for the UTC discussion of the initial
Line_Break property values 15 years ago was:


and the corresponding table draft (before approval and conversion
into the final format that was published with UTR #14 -- later
/UAX/ #14) was:


There is nothing different or surprising in terms of values there. The 
katakana were lb=AL and the fullwidth katakana were lb=ID in
that earliest draft, as of 1999.

What is new information, perhaps, is the explicit correlation that can 
be found
in those documents with the East_Asian_Width properties, and the explanation
in L2/99-179 that the EAW property values were explicitly used to
make distinctions for the initial LB values.

There is no sample text or expected layout results from that time period,
because that was not the basis for the original UTC decisions on any of 
Initial LB values were generated based on existing General_Category
and EAW values, using general principles. They were not generated by
examining and specifying in detail the line breaking behavior for
every single script in the standard, and then working back from those
detailed specifications to attempt to create a universal specification
that would replicate all of that detailed behavior. Such an approach
would have been nearly impossible, given the state of all the data,
and might have taken a decade to complete.

That said, Japanese line breaking was no doubt considered as part of
the overall background, because the initial design for UTR #14 was informed
by experience in implementation of line breaking algorithms at Microsoft
in the 90's.

> You commented that the UAX#14 class should not be changed but
> the tailoring of the line breaking behaviour would solve
> the problem (as Firefox and IE11 did). However, some developers
> may wonder "there might be a reason why UTC put halfwidth-katakana
> to AL - without understanding it, we could not determine whether
> the proposed tailoring should be enabled always, or enabled
> only for a specific environment (e.g. locale, surrounding text)".

See above, in L2/99-179. *That* was the justification. It had nothing
to do with specific environment, locale, or surrounding text.

> If UTC can supply the "expected layout result for halfwidth-
> katakana (used to define the class in current UAX#14)", it
> would be helpful for the developers to evaluate the proposed
> tailoring algorithm.

UAX #14 was never intended to be a detailed, script-by-script
specification of line layout results. It is a default, generic, universal
algorithm for line breaking that does a decent, generic job of
line breaking in generic contexts without tailoring or specific
knowledge of language, locale, or typographical conventions in use.

UAX #14 is not a replacement for full specification of kinsoku
rules for Japanese, in particular. Nor is it intended as any kind
of replacement for JIS X 4051.

Please understand this: UAX #14 does *NOT* tell anyone how
Japanese text *should* line break. Instead, it is Japanese typographers,
users and standardizers who tell implementers of line break
algorithms for Japanese what the expectations for Japanese text should
be, in what contexts. It is then the job of the UTC and of the
platform and application vendors to negotiate the details of
which part of that expected behavior makes sense to try to
cover by tweaking the default line-breaking algorithm and the
Line_Break property values for Unicode characters, and which
part of that expected behavior makes sense to try to cover
by adjusting commonly accessible and agreed upon tailoring
behavior (or public standards like CSS), and finally which part of that
expected behavior should instead be addressed by value-added, proprietary
implementations of high end publishing software.



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://unicode.org/pipermail/unicode/attachments/20150501/fc41dbb1/attachment.html>

More information about the Unicode mailing list