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

18 Chapter 2. Text, Symbols, and Commands
Command names are case sensitive, so \large, \Large and \LARGE
are distinct commands.
Many commands operate on some short piece of text, which then
appears as an argument in curly braces following the command name.
For example, \emph{stress} is given to print the word stress in an
emphasized typeface (here italic) as stress. Such arguments are said to be
mandatory because they must always be given.
Some commands take optional arguments, which are normally employed
to modify the effects of the command somehow. The optional
arguments appear in square braces.
In this book we present the general syntax of commands as
\name[optional]{mandatory}
where typewriter characters must be typed exactly as illustrated and
italic text indicates something that must be substituted for. Optional
arguments are put into square brackets [ ] and the mandatory ones into
curly braces { }. A command may have several optional arguments, each
one in its set of brackets in the specified sequence. If none of the optional
arguments is used, the square brackets may be omitted. Any number of
blanks, or even a single new line, may appear between the command name
and the arguments, to improve legibility.
Some commands have several mandatory arguments. Each one must
be put into a { } pair and their sequence must be maintained as given in
the command description. For example,
\rule[lift]{width}{height}
produces a black rectangle of size width and height, raised by an amount
lift above the current baseline. A rectangle of width 10 mm and height
3 mm is made with \rule{10mm}{3mm}. Since the optional argument lift
is omitted, the rectangle is set on the baseline with no lifting, as .
The arguments must appear in the order specified by the syntax and may
not be interchanged.
Some commands have a so-called *-form in addition to their normal
appearance. A * is added to their name to modify their functionality
somehow. For example, the \section command has a *-form \section*
which, unlike the regular form, does not print an automatic section number.
For each such command, the difference between the normal and
*-form will be explained in the description of the individual commands.
Command names consist only of letters, with the first non-letter indicating
the end of the name. If there are optional or mandatory arguments
following the command name, then it ends before the [ or { bracket,
since these characters are not letters. Many commands, however, possess
no arguments and are composed of only a name, such as the command
\LaTeX to produce the L AT E X logo. If such a command is followed by