Generic Collection Editor?

All, I'm having problem understanding how to customize Magritte/Seaside. I have an object PXADataType with the following description: descriptionValues ^ MAToManyRelationDescription new classes: (Array with: PXAQuantityValue with: PXAQualityValue); accessor: #values; label: 'Werte'; priority: 100; beDefinitive; beOrdered; yourself This object has a collection of values accessible by #values where the collection items can be of type PXAQuantityValue or PXAQualityValue. When I call: an edit form on PXADataType using "(aPXADataType descriptionEdit asComponentOn: aPXADataType) addValidatedForm" I do get the values rendered as a report. However the only possibility to edit the collection is by changing the order using "up"/"down". What I would like to do is a extended report with a possibility to add/change/delete the entries? How can I change the default behaviour in this case? Thanks for your help. CU, udo