diff -r 13890356df78 -r 7a53fc156c2b src/Pure/PIDE/markup.scala
--- a/src/Pure/PIDE/markup.scala	Fri Jul 10 21:58:49 2020 +0200
+++ b/src/Pure/PIDE/markup.scala	Fri Jul 10 22:38:03 2020 +0200
@@ -576,6 +576,9 @@
   object Command_Timing extends Properties_Function("command_timing")
   object Theory_Timing extends Properties_Function("theory_timing")
   object Session_Timing extends Properties_Function("session_timing")
+  {
+    val Threads = new Properties.String("threads")
+  }
   object ML_Statistics extends Properties_Function("ML_statistics")
   object Task_Statistics extends Properties_Function("task_statistics")