DeleteSet - Delete all collection instances (Ctrl+Del)
 The delete set action will be activated for controls referring to owning collections, only. When the data source is not a reference or relationship or when the collection does not own its instances, the action is inactive (hidden) and cannot be called.
The delete set action will be activated for controls referring to owning collections, only. When the data source is not a reference or relationship or when the collection does not own its instances, the action is inactive (hidden) and cannot be called. 
When list items are available read-only, the action is disabled.
When calling the action, it will delete all listed instances from the database without warning or message. In order to receive a warning message before deleting an instance the GUIFramework.Query.Delete option should be set (see "Option browser").
When a selection has been set for the list, items fulfilling the selection criteria (visible items) are removed, only.

