IPA's double life (RE: New scripts)

[Don Osborn]

>Michael Everson wrote:
...
> There are many, many, many Latin letters in the UCS. Some of them are
> used in the IPA.


To look at this another way, a number of characters in the IPA Extensions
range are also used in orthographies of various languages, such as many in
Africa.

Hence it is confusing for people asking "Where's my character?" for one of
these orthographies on the Unicode site to have IPA Extensions separated out
from the Latin group on http://www.unicode.org/charts/ and buried partway
down another page linked under "(see also Phonetic Symbols)." I realize this
particular example is not the concern of this list, but mention it as a
preface to the following remarks.

IPA Extensions, or at least some characters in it, in effect lead a double
life: as symbols for phonetic transcription and as parts of orthographies of
living languages.

So, several questions re ISO 15924:
1) Is IPA Extensions range covered as a general rule in Latn? This wasn't
evident from http://www.unicode.org/iso15924/iso15924-codes.html and other
pages I scanned on unicode.org. In looking at some back correspondence on
ietf-languages it seems that it is.
2) Is there any precedent for specific characters or ranges in Unicode to be
covered by more than one ISO 15924 code? I believe I recall there are a few
cases, but that they are exceptions.
3) Are there rules on the use of phonetic transcription per the
International Phonetic Association or other authoritative body that might
make it reasonable to treat it as an "orthography" in the way that Zmth or
Zsym are?

The main point is that IPA Extensions are both part of extended Latin and
part of phonetic symbols. The main question is whether the latter role
merits a separate script code.

Don