20.1. TeX and LaTeX

T_EX is a professional text processing system for all kinds of documents, articles, and books—especially those that contain a great deal of mathematics. It is a somewhat "low-level" text processing language because it describes to the system how to lay out text on the page, how it should be spaced, and so on. T_EX doesn't concern itself directly with higher-level elements of text such as chapters, sections, footnotes, and so forth (those things that you, the writer, care about the most). For this reason, T_EX is known as a functional text-formatting language (referring to the actual physical layout of text on a page) rather than a logical one (referring to logical elements, such as chapters and sections). T_EX was designed by Donald E. Knuth, one of the world's foremost experts in programming. One of Knuth's motives for developing T_EX was to produce a typesetting system powerful enough to handle the mathematics formatting needed for his series of computer science textbooks. Knuth ended up taking an eight-year detour to finish T_EX; most would agree the result was well worth the wait.

Of course, T_EX is very extensible, and it is possible to write macros for T_EX that allow writers to concern themselves primarily with the logical, rather than the physical, format of the document. In fact, a number of such macro packages have been developed—the most popular of which is LAT_EX, a set of extensions for T_EX designed by Leslie Lamport. LAT_EX commands are concerned mostly with logical structure, but because LAT_EX is just a set of macros on top of T_EX, you can use plain commands as well. LAT_EX greatly simplifies the use of T_EX, hiding most of the low-level functional features from the writer.