Select the active page that this page refers. This is used when this page is a sub-page but you want to trigger the active state of an item from the main navigation bar to which this page is not directly linked. This can be done by selecting the main page of this sub-page from the drop down list. Normally there is also a secondary navigation bar on this sub-page and the active state of one of the items on the secondary navigation bar is already triggered. After adding the reference, the active state of the items on the secondary navigation bar and on the main navigation bar will both be triggered.
