<code>\usepackage[<package-option-list>]{<package-list>}[<version>]</code>//There can be any number of these declarations. All packages in <code><package-list></code> are called with the same options.//Each <code><package></code> file defines new elements (or modifies those defined in the <code><class></code>), and thus extends the range of documents which can be processed. The <code><package-option-list></code> is a list of options which can modify the formatting of elements defined in the <code><package></code> file. The <code><version></code> is a version number, beginning with a date in the format <code>YYYY/MM/DD</code>. If an older version of the package is found, a warning is issued.