Guide to LaTeX (4th Edition) (Tools and Techniques

2
Text, Symbols, and
Commands
The text that is to be the input to a L AT E X processing run is written to a
source file with a name ending in.tex, the file name extension. This file is
prepared with a text editor, either one that handles straightforward plain
text, or one that is configured to assist the writing and processing of L AT E X
files. In either case, the contents of this file are plain ascii characters
only, with no special symbols, no accented letters, preferably displayed in
a fixed width typewriter font, with no frills like bold or italics, all in one
size. All these aspects of true typesetting are produced afterwards by
the T E X processing program with the help of markup commands inserted
visibly into the actual text. It is therefore vital to know how commands
are distinguished from text that is to be printed, and, of course, how they
function.
(However, for languages other than English, native keyboard input may
indeed be used, as shown in Section 2.5.9.)
2.1 Command names and arguments
A command is an instruction to L AT E X to do something special, like print
some symbol or text not available to the restricted character set used
in the input file, or to change the current typeface or other formatting
properties. There are three types of command names:
• the single characters # $ & ˜ _ ˆ % { } all have special meanings
that are explained later in this chapter;
• the backslash character \ plus a single non-letter character; for
example \$ to print the $ sign; all the special characters listed above
have a corresponding two-character command to print them literally;
• the backslash character \ plus a sequence of letters, ending with the
first non-letter; for example, \large to switch to a larger typeface.
17