For years we've had our own custom configuration library and I decided we should try to switch to Aero -- and was shocked at how easy it was! We had a #worldsingles.configuration/include tag that turned out to have the exact same semantics as the adaptive-resolver in Aero so I just added a defmethod for that that which delegated to Aero's 'include and that was it: everything just worked straight away! And now we get environment variables for free. Now I just need to figure out how to migrate our even older, even more custom "environment" library 🙂