The \gls*{preamble} is the part of the \gls{source} that comes
after the \screenlinebreak\reportlinebreak\glsi{documentclass}
\gls{command} and before
\glsni{begin}\marg{\texttt{document}} (the start of the
\glsi{env-document} \gls{environment}).  Only
a few
special commands may be placed in the preamble (such as \glsni{title}), and there are a few
special commands that may only go in the preamble (such as \glsi{usepackage}).
Nothing that generates text (for example, \glsi{maketitle}) may go in the preamble.

\preambleillustration