src/Pure/PIDE/headless.scala

     def default_check_delay: Time = session_options.seconds("headless_check_delay")
     def default_check_limit: Int = session_options.int("headless_check_limit")
     def default_nodes_status_delay: Time = session_options.seconds("headless_nodes_status_delay")
     def default_watchdog_timeout: Time = session_options.seconds("headless_watchdog_timeout")
     def default_commit_cleanup_delay: Time = session_options.seconds("headless_commit_cleanup_delay")
+
+    def show_states: Boolean = session_options.bool("show_states")
 
 
     /* temporary directory */
 
     val tmp_dir: JFile = Isabelle_System.tmp_dir("server_session")