Q: [previous Q&A] …I have a question about the usage of your typographic programs in commercial institutions like DTP [desktop publishing] studios and so on. I’d like to ask about using parts of the T_eX source. You made clear that the programmers were free to incorporate parts of the T_eX source into their own programs. There are some remarkable examples of this, do you know.
D. Knuth: That question came up also last summer when I had a [1995_29ya] question-and-answer session at the [1995_29ya] TUG meeting in Florida. I thought it would be fairly common to have special versions of T_eX. I designed T_eX so that it has many hooks inside; you can write extensions and then have a much more powerful T_eX system readily adapted…A macro language is Turing-complete—it can do anything—but it’s certainly silly to try to do everything in a high-level language when it’s so easy to do it at the lower level. Therefore I built in hooks to T_eX and I implemented parts of T_eX as demonstrations of these hooks, so that a person who read the code could see how to extend T_eX to other things. We anticipated certain kinds of things for chemistry or for making changebars [colored lines indicating modified sections of text, like a visual diff] that would be done in the machine language for special applications. Certainly, if I were a publishing house, if I were in the publishing business myself, I would have probably had 10 different versions of T_eX by now for 10 different complicated projects that had come in. They would all look almost the same as T_eX, but no one else would have this program—they wouldn’t need it, they’re not doing exactly the book that my publishing house was doing.

That was what I thought would occur. And certainly, there was a point in the middle-1980s when there were more than a thousand people in the world that knew the T_eX program, that knew the intricacies of the T_eX program quite well. They had read it, and they would have been able to make any of these extensions if they wanted. Now I would say that the number of people with a working knowledge of T_eX’s innards is probably less than a thousand, more than a hundred. It hasn’t developed to the extent that I expected…Anyway, I made it possible to do very complicated things. When you have a special application, I was always expecting that you would want to have a specially tuned program there because that’s where it’s easiest to do these powerful things.

…My general philosophy with T_eX was to try to have a system that covers 99% of all cases easily [laughter]; and I knew there would always be a residual number. But I felt that this residual would only be needed by the people who really care about their papers, and then if they’re only spending 1% of the time on this, then they would enjoy feeling that they had contributed something special by adding their little signature, their special character to it. So, I didn’t try to do everything automatically.

[cf. 1995 in Florida: “…It’s certainly what I would have done! If I were putting out a Bible or something, if I were a publisher with some project that I wanted to do specially well, then I would want a special typesetting tool for it. Rewriting a typesetting system is fairly easy.” [laughter]]