## 4.5 Making Your Own Documents with HTML

In the days before computerized word processing systems, authors used a standard set of symbols to mark drafts of books and papers to let typesetters know how to change the draft. Authors who use a computer-based text formatter also use a well-defined set of symbols. These symbols, which comprise a mark-up language, are embedded in the paper along with the text. A text formatter works very much like a compiler, reading a program'' written in the mark-up language and generating output for a laser writer or bitmap display. Well- known examples of text formatting systems based on mark-up languages are nroff and troff (early Unix programs) and LaTeX.

As an example, suppose you want to produce the following sentence in a document:

The input to LaTeX that would generate this line is:

There are $a^n$ possible {\it n}-letter
words constructed from an alphabet of {\it a} symbols.