diff -r f2a10986e85a -r 00be8711082f src/Pure/General/markup.scala
--- a/src/Pure/General/markup.scala	Wed Sep 22 12:52:35 2010 +0200
+++ b/src/Pure/General/markup.scala	Wed Sep 22 13:47:48 2010 +0200
@@ -227,7 +227,6 @@
 
   /* messages */
 
-  val PID = "pid"
   val Serial = new Long_Property("serial")
 
   val MESSAGE = "message"