--- a/src/Pure/PIDE/xml.scala Thu Feb 20 14:17:28 2014 +0100
+++ b/src/Pure/PIDE/xml.scala Thu Feb 20 14:36:17 2014 +0100
@@ -7,6 +7,7 @@
package isabelle
+
import java.util.WeakHashMap
import java.lang.ref.WeakReference
import javax.xml.parsers.DocumentBuilderFactory