_isActiveAncestor() {
		const currentState = this._routing.currentState;
		/* istanbul ignore next */
		if ( !currentState ) {
			return false;
		}

		/** @type {{name: string}[]} */
		const { routeInfos } = currentState.routerJsState;
		const routeInfosAncestors = routeInfos.slice( 0, -1 );
		const routeInfosLeafName = routeInfos[ routeInfos.length - 1 ].name;
		const routeName = this.qualifiedRouteName;

		return routeInfosLeafName !== routeName
		    && routeInfosLeafName !== `${routeName}.index`
		    && routeInfosAncestors.find( ({ name }) => name === routeName );
	}
Checks whether the link is active because of an active child route.
The `current-when` property which overrides the active state is not supported, since it's
not being used in this project (at this present time).
@returns {boolean}