Re: Merging combining classes, was: New contribution N2676

From: Jim Allan (
Date: Wed Oct 29 2003 - 08:02:28 CST

Peter Kirk wrote:

> Rather, it defines that they do not. But since this is not true on any
> reasonable intuitive definition of "interact typographically" (as we
> have seen with Hebrew vowel points), this statement makes sense only as
> a counterintuitive definition of "interact typographically".

Exactly. The words in the standard don't fit the facts, though one can
read through the words and understand what is meant.

 From 4.3:

<< For example, it is crucial that the combining class of the cedilla be
lower than the combining class of the dot below, although their exact
values of 202 and 220 are not important for implementation. >>

This is not explained, but obviously the reason why it is "crucial" that
the combining class of cedilla be lower is that the cedilla indeed might
interact with characters in other combining classes and so must belong
to a combining class which is applied first so that other diacritics
that might be applied beneath are positioned below the cedilla which
cannot have any other diacritic between it and the base character.

> The implication is that a font designer
> cannot assume that glyph positioning adjustments are required only
> between adjacent characters in canonical order, despite what the
> "interact typographically" rule might suggest.

Therefore the standard should so indicate. Currently it really says the
opposite, though that obviously isn't right and not what is intended.

Jim Allan

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