Load ordinary overlays without a main source

source.go

@@ -49,8 +49,7 @@ func Mapping(label string, values map[string]any) Source {
 
 // NoSource selects an absent input for defaults and resolution. It creates no
 // source record and has no main declarations to traverse when imports are enabled.
-// An explicit filesystem context may be supplied; active overlays are not
-// available for absent inputs.
+// An active overlay requires explicit filesystem context.
 func NoSource() Source { return Source{value: engine.NoSource()} }
 
 func (s Source) toEngine() engine.Source { return s.value }