How does one use the NavigationMenu parameter in a custom navigation component? We have a custom navigation menu aura component extending forceCommunity:navigationMenuBase but none of the parameters show up that would allow me to indicate one of the Navigation Menu's defined in the community like the standard Navigation components have in the OOB themes.

It's mentioned here: https://releasenotes.docs.salesforce.com/en-us/winter20/release-notes/rn_networks_nav_menu_variations.htm that "create custom navigation menu components that are based on existing menus". 

Can someone please advise?