In the LaTeX input file, a command name starts with a backslash
character, \. The name itself then consists of either
(a) a string of letters or (b) a single non-letter.
LaTeX commands names are case sensitive; for example,
\pagebreak differs from \Pagebreak (the latter is not a
standard command). Most command names are lowercase, but in any event
you must enter all commands in the same case as they are defined.
A command may be followed by zero, one, or more arguments. These
arguments may be either required or optional. Required arguments are
contained in curly braces, {...}. Optional arguments are
contained in square brackets, [...]. Generally, but not
universally, if the command accepts an optional argument, it comes
first, before any required arguments; optional arguments could come
after required arguments, or both before and after.
Inside of an optional argument, to use the character close square
bracket (]) hide it inside curly braces, as
in \item[closing bracket {]}]. Similarly, if an optional
argument comes last, with no required argument after it, then to make
the first character of the following text be an open square bracket,
hide it inside curly braces.
LaTeX has the convention that some commands have a * form
that is closely related to the form without a *, such as
\chapter and \chapter*. The difference in behavior
varies from command to command.
This manual describes all accepted options and *-forms for the
commands it covers (barring unintentional omissions, a.k.a. bugs).
As of the 2020-10-01 release of LaTeX, the expl3 and
xparse packages are part of the LaTeX2e format. They
provide a completely different underlying programming language
syntax. We won’t try to cover that in this document; see the related
package documentation and other LaTeX manuals.