src/Pure/Tools/isabelle_process.ML

       (case try XML.tree_of_string (XML.element "message" [] [raw_txt]) of
         NONE => (raw_txt, Position.none)
       | SOME xml => (XML.plain_content xml, the_default Position.none (get_pos xml)))
       |>> translate_string (fn c => if c = STX then DEL else c);
     val props =
-      (case Position.properties_of (Position.thread_data ()) of
-        [] => Position.properties_of pos
-      | props => props);
+      Position.properties_of (Position.thread_data ())
+      |> Position.default_properties pos;
   in Output.writeln_default (special ch ^ print_props props ^ txt ^ special_end) end;
 
 fun init_message () =
   let
     val pid = ("pid", string_of_pid (Posix.ProcEnv.getpid ()));