README_V3.md in schemacop-3.0.20 vs README_V3.md in schemacop-3.0.21

@@ -871,9 +871,12 @@
   properties are allowed (i.e. they pass the validation), but they are removed
   from the result hash. This is useful e.g. to validate params coming from the
   controller, as this only allows white-listed params and removes any params
   which are not whitelisted (i.e. similar to strong params from Rails).
 
+  If it is set to an enumerable (e.g. `Set` or `Array`), it functions as a
+  white-list and only the given additional properties are allowed.
+
 #### Specifying properties
 
 Hash nodes support a block in which you can specify the required hash contents.
 
 ##### Standard properties