I poured through the source code and discovered how the module Role Layer Rule - Version: 1.0 works.
It is quite simple really and similar to how the URL filter works ( See "Managing Widgets" (http://orchardproject.net/docs/Managing-widgets.ashx) )
Suppose you had a role MyFriends, and you wanted a Layer that was active for MyFriends on the homepage only. You would write the rule as:
role("MyFriends") and url("~/")
Hopefully this will help someone else who wants to use this module.