src/Pure/PIDE/document.scala

         if name == file_name
       } yield cmd).toList
 
     def descendants(names: List[Node.Name]): List[Node.Name] = graph.all_succs(names)
     def topological_order: List[Node.Name] = graph.topological_order
+
+    override def toString: String = topological_order.mkString("Nodes(", ",", ")")
   }
 
 
 
   /** versioning **/