AET Create Application Reference Custom Field

I'm trying to understand the AET data type "NAV_OBJECT Application Reference".  I can't find any documentation on how to use it except this:

"If you have selected Application Reference as the field type, the field is displayed as a hyperlink that allows you to navigate to an object (business object)."

Does anyone know how this works?  How do you set the link? 

Are you restricted to the objects in the sub-types?  Could I link to a specific note for example?

Thanks,

Clint