Hello Adam,
[cc to IETF LTRU WG]
On 2009/10/30 16:12, Adam Twardoch (List) wrote:
III. LANGUAGE CLASSIFICATION
All OpenType Layout features are assigned in a context of specific
script and language system. While the assignment of script is easy (the
engine can determine from the Unicode string which script a certain
character belongs to, and from there it can pick the appropriate
OpenType script branch to apply the features for), the language system
is trickier.
As you can see from
http://www.microsoft.com/typography/otspec/languagetags.htm
OpenType uses a list of language systems that do not have a 1:1
correspondence with any of the ISO 639 standards. In OpenType 1.6 (at
the link above), an informational mapping of OpenType language system
tags and "best matches" in the ISO 639 standards has been provided. It
is quite obvious that a web browser that applies OpenType Layout
features should observe the HTML "lang" attribute and, if present, apply
the appropriate features from the particular language system branch in a
font (and only if absent, apply the features from the Default language
system within a script branch). But it might be worth considering to add
a low-level CSS access mechanism to allow users to choose a specific
OpenType language system, because some ISO 639 codes can map to several
OpenType language systems, e.g.
(OT) (ISO)
Chinese Hong Kong ZHH zho
Chinese Phonetic ZHP zho
Chinese Simplified ZHS zho
Chinese Traditional ZHT zho
HTML lang and XML xml:lang use BCP 47 (http://tools.ietf.org/html/bcp47, formerly RFC 1766/3066/4646) tags, not ISO 639 directly. BCP 47 uses two-letter codes (i.e. 'zh') and not three-letter codes (i.e. 'zho') when two-letter codes are available. Also, BCP 47 has facilities for indicating Region (country,...) with two-letter codes and for indicating script with four-letter codes. So the above list should be changed to:
(OT) (BCP 47)
Chinese Hong Kong ZHH zh-HK
Chinese Phonetic ZHP **
Chinese Simplified ZHS zh-Hans
Chinese Traditional ZHT zh-Hant
** not sure what's meant by Chinese Phonetic, may be zh-Latn (Latin transcription) or zh-Bopo (Bopomofo)?
Regards, Martin.
--
#-# Martin J. Dürst, Professor, Aoyama Gakuin University
#-# http://www.sw.it.aoyama.ac.jp mailto:duerst at it.aoyama.ac.jp
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