The MED editor currently requires the user to type in the fully qualified Java class name of the metaclass being extended. The editor should instead provide a set of all available metaclass names to the user to choose from. This is the way the extension model framework being replaced worked. Since metaclasses can have containment associations those relationships should be shown in a tree form. One way of providing these metaclass names would be to add the requirement to the extension point that identifies the extendable metamodels. For instance, each extension could provide an instance of interface that has a method like "getExtendableMetaclasses()." The editors metaclass dialog would need to be changed to provide a Tree UI object to choose the metaclass name.