Answer prose round 1: the custom-CLI test advice says why an indexed module needs each path rendered, the help ruling says the help points to --list and who ruled, ErrNoColumns's doc says what it matches, and the filed items read in one pass

fejkdata.go

@@ -92,8 +92,8 @@ func (loadError) Is(target error) bool { return target == ErrLoad }
 // winning a name clash; it fails where no [WithDataFS] or [WithDataPath] names the data
 // to load. Each JSON file becomes a category named after the file (address.json ->
 // "address") and each subdirectory a namespace segment. It errors on a missing
-// directory, invalid JSON or invalid data. WithDataFS() alone loads no data, and the
-// generator renders templates that read none. A source whose .fejkdata.json carries an
+// directory, invalid JSON or invalid data. Given only WithDataFS() with no modules, New
+// loads no data, and the generator renders templates that read none. A source whose .fejkdata.json carries an
 // index, as each shipped module's does, loads each category on the first call reaching
 // it. Data failing to load, in New or on that first call, gives an error matching
 // [ErrLoad].