[tex-k] TeXbook: space -> control space

[Karl Berry]

Hi Igor,

    It is still not clear to me from the TeXbook why it is "usually wise".

My guess is that Knuth simply didn't want to write a blanket statement
("always type a ~"). That would have felt too draconian.

    (i.e., is there any counter-example to "usually" and an example when
    it can be "unwise")

The only case I can think of is when the tie causes an overfull line and
there's no other reasonable fix at hand. In that case I would accept a
line break after an abbreviation.

        but not before `|---|'; cf.\ Appendix~H\null. The ^|\relax| ...

There's no reason not to use a ~ after the "cf." there.  Personally I
think a ~ would be preferable.

Knuth does not try to make his books perfectly, 100%, absolutely
consistently, follow everything he prescribes, especially the .tex
sources for them. Since the "cf." does not fall at the end of the line
in the printed book, he probably never even thought about it. If it did,
I feel sure he would have changed it to a tie. --best, karl.