src/Pure/PIDE/document.scala

         (_, node) <- iterator
         cmd <- node.load_commands.iterator
         name <- cmd.blobs_names.iterator
         if name == file_name
       } yield cmd).toList
+
+    def undefined_blobs: List[Node.Name] =
+      (for {
+        (_, node) <- iterator
+        cmd <- node.load_commands.iterator
+        name <- cmd.blobs_undefined.iterator
+      } yield name).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(", ",", ")")