These are commands designed to help writers of classes or packages.
\AtBeginDvi
& \AtEndDvi
\AtEndOfClass
& \AtEndOfPackage
\CheckCommand
\ClassError
and \PackageError
and others\CurrentOption
\DeclareOption
\DeclareRobustCommand
\ExecuteOptions
\IfFileExists
& \InputIfFileExists
\LoadClass
& \LoadClassWithOptions
\NeedsTeXFormat
\OptionNotUsed
\PassOptionsToClass
& \PassOptionsToPackage
\ProcessOptions
\ProvidesClass
& \ProvidesPackage
\ProvidesFile
\RequirePackage
& \RequirePackageWithOptions