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

[Karl Berry]

        In fact, it's usually wise to type |~| (instead of a space) 

I'm pretty certain that Knuth intended a normal space this early in the
book, because that is what new users would think to type. Although the
concept of control spaces has been introduced, he is still explaining
things to people encountering TeX for the first time here.

He could have said "a space or control space", but he didn't, and I see
no chance he would want to make such a change at this late date. --best, karl.