diff -r c54498f88a77 -r 1d33e85a3fa9 src/Pure/General/markup.scala
--- a/src/Pure/General/markup.scala	Fri Dec 04 22:51:59 2009 +0100
+++ b/src/Pure/General/markup.scala	Sat Dec 05 16:39:49 2009 +0100
@@ -40,6 +40,11 @@
   val LOCATION = "location"
 
 
+  /* hidden text */
+
+  val HIDDEN = "hidden"
+
+
   /* logical entities */
 
   val TCLASS = "tclass"