comment why one should not try to modify the returned dict in place

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@32200 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Resource.py

@@ -869,6 +869,8 @@ class Resource(XMLMatrix, Variated):
       global_definition_dict = self.\
           QuantityUnitConversionModule_getUniversalDefinitionDict()
 
+      # _getUniversalDefinitionDict is a cached function. Copy the object to
+      # avoid modifying it
       result = global_definition_dict.copy()
       for definition_group in self.objectValues(portal_type= \
           'Quantity Unit Conversion Group'):