[XeTeX] Polytonic greek and XeLaTeX

[Jonathan Kew]

On 2 Jan 2008, at 3:35 pm, Apostolos Syropoulos wrote:

>> The correct way to produce Ὀ (GREEK CAPITAL LETTER OMICRON WITH
>> PSILI, U+1F48) would be to use Ο  (GREEK CAPITAL LETTER OMICRON, U
>> +039F) with ᾿ (COMBINING COMMA ABOVE, U+0313), which is faked here
>> with GREEK PSILI at U+1FBF. The combining effect already failed for
> What do you mean by "correct"?

According to the Unicode standard, <U+1F48 GREEK CAPITAL LETTER  
OMICRON WITH PSILI> is canonically equivalent to the sequence <U+039F  
GREEK CAPITAL LETTER OMICRON, U+0313 COMBINING COMMA ABOVE>. So  
Unicode-compliant fonts and software that fully support these  
characters should render them indistinguishably, and indeed software  
is free to convert between the precomposed and decomposed  
representations at any time, without affecting the meaning of the data.

> BTW, a psili, and for that mater a dasia,
> is not a comma above.

True, but that is nevertheless the name of the character used as the  
diacritic. Exactly what it looks like (and how it is positioned in  
relation to the base character -- in the case of Greek capitals, it  
is not actually "above") is a matter for font designers to get right.  
Unicode/ISO10646 character names are just standardized identifiers;  
they may not always be descriptively accurate.

> Also, Greek speaking people do prefer the pre-built
> glyph instead of what you propose.

With adequate Unicode support in the software and fonts, users should  
not be able to tell whether the internal representation is <U+039F, U 
+0313> or simply <U+1F48>.

It's true that many current products fall short of this ideal, though.

U+1FBF GREEK PSILI is a different matter; this is a "spacing" version  
of the mark, and should not normally be used in text, as far as I  
know. I suppose it could be useful when writing about the diacritic  
itself, rather than using it in combination with a vowel.

JK