more markup elements;

--- a/src/Pure/General/markup.scala	Sun Dec 28 16:39:27 2008 +0100
+++ b/src/Pure/General/markup.scala	Sun Dec 28 20:25:39 2008 +0100
@@ -93,6 +93,10 @@
   val CONTROL = "control"
   val MALFORMED = "malformed"
 
+  val COMMAND_SPAN = "command_span"
+  val IGNORED_SPAN = "ignored_span"
+  val MALFORMED_SPAN = "malformed_span"
+
 
   /* toplevel */