Module_Manager::register( string $slug, string $module_class_name )

	public function register( $slug, $module_class_name ) {
		if ( isset( $this->modules[ $slug ] ) ) {
			/* translators: %s: module slug */
			return new Error( $this->get_prefix() . 'module_already_exist', sprintf( __( 'A module with the slug %s already exists.', 'torro-forms' ), $slug ), __METHOD__, '1.0.0' );
		}

		if ( ! class_exists( $module_class_name ) ) {
			/* translators: %s: module class name */
			return new Error( $this->get_prefix() . 'module_class_not_exist', sprintf( __( 'The class %s does not exist.', 'torro-forms' ), $module_class_name ), __METHOD__, '1.0.0' );
		}

		if ( ! is_subclass_of( $module_class_name, Module::class ) ) {
			/* translators: %s: module class name */
			return new Error( $this->get_prefix() . 'module_class_not_allowed', sprintf( __( 'The class %s is not allowed for a module.', 'torro-forms' ), $module_class_name ), __METHOD__, '1.0.0' );
		}

		$this->modules[ $slug ] = new $module_class_name( $this->get_prefix(), array(
			'manager'       => $this,
			'error_handler' => $this->error_handler(),
		) );

		return true;
	}