Joachim Schrod wrote --

> Yes, and Kaeufer has even better examples and some rules. The problem:
> UC kerning (``spationieren'') is not as brute force as letterspacing
> (``sperren''), it is expected to take _the_whole_surrounding_ into
> accout. I.e., the amount of kerning depends also on the typeset
> material that is above or below the text to be kerned, its size, its
> distance, etc.
> That's one of the things in typography where you talk with designers
> and/or typesetters, and they tell you: You just have to see it. The
> formalization of that `seeing' is an open research problem, as far as
> I know.

It is, along with many other aspects of the compositor's craft.