\RequirePackage & \RequirePackageWithOptions ¶Synopsis:
\RequirePackage[option-list]{pkgname}[release-date]
\RequirePackageWithOptions{pkgname}[release-date]
Load a package, like the command \usepackage (see Additional packages). An example:
\RequirePackage[landscape,margin=1in]{geometry}
The initial optional argument option-list, if present, must be a
comma-separated list. The trailing optional argument
release-date, if present, must have the form YYYY/MM/DD.
If the release date of the package as installed on your system is
earlier than release-date then you get a warning like ‘You
have requested, on input line 9, version `2017/07/03' of package
jhtest, but only version `2000/01/01' is available’.
The \RequirePackageWithOptions variant uses the list of options
for the current class. This means it ignores any options passed to it
via \PassOptionsToClass. This is a convenience command to
allow easily building classes on existing ones without having to track
which options were passed.
The difference between \usepackage and \RequirePackage
is small. The \usepackage command is intended to be used in
documents, while \RequirePackage is intended for package and
class files. The most significant difference in practice is that
\RequirePackage can be used in a document before the
\documentclass command, while \usepackage gives an error
there. The most common need for this nowadays is for the
\DocumentMetadata command (see \DocumentMetadata: Producing tagged PDF output).
The LaTeX development team strongly recommends use of these and
related commands over plain TeX’s \input; see the Class
Guide (https://ctan.org/pkg/clsguide).