From: Jukka K. Korpela (jkorpela@cs.tut.fi)
Date: Sun May 21 2006 - 23:47:38 CDT
On Sun, 21 May 2006, Kent Karlsson wrote:
> Because it is in ISO/IEC 8859. Hadn't ISO/IEC 8859-1 been so
> commonly supported, MICRO SIGN would have been canonically
> equivalent with GREEK SMALL LETTER MU.
Why? How did the common support to ISO/IEC 8859-1 dictate the decision
that was made? It would have been possible to make these characters
canonically equivalent or even the same, although it would have been
somewhat odd to have a Greek letter in the Latin 1 Supplement block and a
corresponding hole in the Greek block. As far as I can see, it was a
practical decision. It looks like a natural decision to me, since the
glyphs for these characters may well be different, and the MICRO SIGN can
be seen as a special symbol historically based on GREEK SMALL LETTER MU
rather than just its specialized usage.
>> The present justification is that U+00B5 does not belong to
>> any script, whereas U+03BC is in the Greek script.
>
> That's a mistake. It should be in the Greek script, of course,
U+00B5 has the Script value of Common, which might perhaps more
appropriately be characterized as belonging to _any_ script rather than
not belonging to any script. What its script _should_ be is less obvious,
but since it is only compatibility equivalent to a Greek letter, the
current situation looks natural. Similarly, for example, ALEF SYMBOL is in
the Common script, not in the Hebrew script.
> just like the OHM SIGN (which is canonically equivalent with
> GREEK CAPITAL OMEGA;
The OHM sign _is_ in the Greek script, and this is apparently based on its
being _canonically_ equivalent to a Greek letter (which was a somewhat odd
decision, but let's not go into that now).
> the latter of course the preferred
> character to denote the ohm unit symbol,
Yes, there is an explicit statement about that in the Unicode standard.
> just like GREEK SMALL
> LETTER MU is the preferred character for denoting the
> micro unit prefix symbol).
Have you found such a statement, or even an implicit preference, in the
Unicode standard, or some other standard? (Unfortunately, standards
related to the SI, as many other standards, define the use of characters
without identifying them by Unicode numbers or names. Historically, this
is understandable, but it creates considerable vagueness in some cases.)
-- Jukka "Yucca" Korpela, http://www.cs.tut.fi/~jkorpela/
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