public function expandMiddlewareMolecule( $middleware ) {
		$pieces = explode( ':', $middleware, 2 );

		if ( count( $pieces ) > 1 ) {
			return [array_merge( [$this->expandMiddlewareAtom( $pieces[0] )], explode( ',', $pieces[1] ) )];
		}

		if ( isset( $this->middleware_groups[ $middleware ] ) ) {
			return $this->expandMiddlewareGroup( $middleware );
		}

		return [[$this->expandMiddlewareAtom( $middleware )]];
	}