Render a repeat iteration in no group, refuse a group that names nothing, key group names by category, and own reference overlap in one fence

graph.go

@@ -196,7 +196,11 @@ func checkRenders(s nodeScope) error {
 	if err := s(heldCheck); err != nil {
 		return err
 	}
-	if err := s((&drawCheck{}).check); err != nil {
+	fence := &drawCheck{}
+	if err := s(fence.checkGroup); err != nil {
+		return err
+	}
+	if err := s(fence.checkDraws); err != nil {
 		return err
 	}
 	return s((&valueProof{}).checkDatatype)