Index: src/AST/porting.md
===================================================================
--- src/AST/porting.md	(revision 923d25a0481c54f984b2f8571ec487e9042389ca)
+++ src/AST/porting.md	(revision d1ee9ec12dacaf319a5010a5446241854fcc1353)
@@ -47,4 +47,9 @@
       template<typename node_t>
       friend node_t * mutate(const node_t * node);
+      template<typename node_t>
+      friend node_t * shallowCopy(const node_t * node);
+    or equilant.
+* You should use the `mutate` function where possible as it avoids extra copies.
+  * If you must copy use `shallowCopy` or `deepCopy` as required.
 
 All leaves of the `Node` inheritance tree are now declared `final`