As you know, I'm currently looking into adding support for fixed spaces.
This had some effects on the handling of letter- and word-spacing. I've
got word-spacing together with fixed spaces working in the meantime but
I'm tracking down a problem with letter spacing. 7.16.2 says that only
the characters that are marked by Unicode as "Alphabetic" are eligible
for space-start and space-end traits from the letter-spacing property.
I'm trying to come up with an isAlphabetic(char ch) method in
CharUtilities but I'm having trouble there. "Alphabetic"  consists of
characters from several "general categories" and from "Other_Alphabetic".
The general categories are easy (see java.lang.Character's constants and
its getType(char) method). Does anyone have suggestions how best to
identify characters from "Other_Alphabetic"? I found a list in the
Unicode database which lists all the character ranges that make up
Other_Alphabetic but maybe there's already something in Java that I can