From The Document Foundation Wiki
- most of the time, the condition is related to a data source field. Instead of entering the field name, it is possible to drag and drop it from the data source view:
- click the field header then drag and drop it in the Condition area
- do this drag and drop before completing the condition because the drag and drop replaces the content of the preceding area.
- the field will be inserted under the form [Source name.Table name.Field name] so for example [Bibliography.biblio.Identifier]