Answer architecture round 2: a read through a name reaching a repeat names the level from the name, a split arm is built by pathArm alone, and the three pick-key terms share one Vocabulary line

format.go

@@ -152,7 +152,7 @@ func checkArm(name string, fields map[string]node, wholeToken bool) (missing boo
 		}
 		return true, fmt.Errorf("no field %q", a.head)
 	}
-	if err := provePath(field, a.tail, a.head); err != nil {
+	if err := provePath(field, a.tail, a.head, 0); err != nil {
 		return false, fmt.Errorf("field %q: %w", a.head, err)
 	}
 	return false, nil