code: protected void modifyProperties( NodeKey key,
                                       Name primaryType,
                                       Set<Name> mixinTypes,
                                       Map<Name, AbstractPropertyChange> propChanges ) {
      }
docs: Handle the addition, change, and removal of one or more properties of a single node. This method is called once for each
  existing node whose properties are modified.
  
  @param key the unique key for the node; may not be null
  @param primaryType the primary type of the node for which the modifications occurred; never null
  @param mixinTypes the mixin types of the node for which the modifications occurred; never null but possibly empty
  @param propChanges the map of property modification events, keyed by the names of the properties; never null and never