Re: Basic question: types of diacritics marks

From: Kenneth Whistler (
Date: Thu Jul 18 2002 - 20:44:37 EDT

Adam asked:

> I have a very basic question. What would be the implementation differences
> of diacritics marks in a font? For example, we'd consider:
> U+00B4 acute accent
> U+02CA modifier letter acute accent
> U+0301 combining acute accent
> What are the common recommendations regarding the glyphs in a font
> (TrueType), especially with respect to the metrics? Should I support all
> three above codepoints? If so, can I do this with one glyph? Or should I
> provide separate glyphs?

To elaborate on what Michael Everson said, I think the answer here is
that you should probably provide separate glyphs.

U+00B4 would typically have the spacing width of an en, thereabouts, since
it is the spacing clone of a combining mark acute, and on average, you
would expect it to have a en character width. It also gets used for
fallback displays, as for Latin-1 `curly´ quotes using grave and acute
instead of real quotation marks (an extension of ASCII `curly' quotes
using grave and apostrophe), for primes in character sets that don't
really have one (also as an alternate to apostrophe) [cf. U+2032], for
email-type indication of accents on l´et´t´ers´ that you don't have actual
codes for, and the like. So you need to make it look appropriate for
such uses.

U+02CA should typically be a little narrower (I think). It really is a modifier
letter intended to precede or follow a regular letter, usually indicating
a tone or stress for a syllable (as an alternative to the acute actually
placed over a letter in the same function).

And U+0301 needs to be rendered over letters. Its exact placement will
depend on the width and height of the letter it is placed over.

Of course, your mileage may vary, depending on what you are trying to
do with your font design. And John Hudson provided the technical details
regarding what happens inside the font.

> And, briefly, what are the principal differences between the three types of
> marks?

Michael Everson answered this one in terms of functionality.


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