Load ordinary overlays without a main source

internal/engine/load.go

@@ -23,7 +23,8 @@ type Definition[T any] struct {
 // Options contains the application definition and per-load input selections.
 // Imports enables traversal of declarations in a selected main document; an
 // absent source has no main declarations to traverse. Overlay selects one fixed
-// overlay. Overrides contain only values explicitly supplied by an application CLI.
+// overlay and requires filesystem context for NoSource. Overrides contain only
+// values explicitly supplied by an application CLI.
 type Options[T any] struct {
 	Definition              Definition[T]
 	Imports                 bool