Martin J. Dürst wrote:
Thanks for your comments, Martin.
> There can also be triple-byte (and quadruple-byte,...) sets, together
> with double-byte sets called multibyte sets. And these can also be
> 96 x 96 (x 96...).
Are these used in practice?
> Some can have two bytes for designation, or more, in the future.
But not now used in practice, correct?
> Your use of "character set" above is already rather questionable,
> it should be "coded character set". But here it gets more complicated.
When I wrote this, I was not *au courant* with the terminology.
> It's not really the sets that are labeled G0,..., it's the slots they
> can be assigned (designated) to.
A good point, which I should clarify.
> > are labeled G0, G1, G2, and G3. Initially,
> > G0 is the 94-character set ASCII, and G1 is the 96-character set ISO Latin-1
> > (top half).
>
> This is the case in some places, but not at all in general.
This sentence belonged to the original context and should have been
removed for this version.
> To use ISO 2022, you always need a common agreement, or some
> additional introductory ESC sequences.
Are these introductory sequences used in practice?
> It is not really deprecated. It applies to an exactly specified
> set of sets, those that have been registered under the previous
> version of the standard. For these, it is the one that has to
> be used.
Ah. Thanks for this clarification.
> > ISO 2022 decoding affects input bytes in the ranges 33 to 126 and 160 to 255,
> > known as "the left half" and "the right half" respectively. All other bytes,
> > unless they belong to a control sequence shown in this document, remain
> > unchanged.
>
> No. There is a quite similar, although somewhat simpler, system,
> for control character blocks.
I didn't know about this part.
> Also, please note that
> ISO-2022-JP is not in fact conformant to ISO 2022, despite its name,
> because it uses designations only, anew on each line, whereas
> the basic idea of ISO 2022 is to use designations once, or once on
> each line, and then only invocations. This is clearly stated in
> the new version of JIS 208, namely JIS X 0208:1997, Appendix 2
> (normative), Note to item 1.
ISO-2022-JP swaps different character sets in and out of G0.
While this may not be the best practice in some sense, it seems
unlikely to me that it's actually forbidden.
> I still think that for understanding ISO 2022, it's best to look
> at the standard itself.
Until today (special thanks to Werner Lemberg), I didn't know where
ISO 2022 could be obtained except by shelling out $$$$. I'll be
revising my text in accordance with ECMA-35 6th ed., which is
exactly the same as ISO 2022:1994.
-- John Cowan http://www.ccil.org/~cowan cowan@ccil.org e'osai ko sarji la lojban
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