more operations;

--- a/src/Pure/PIDE/xml.scala	Fri Dec 01 20:29:58 2017 +0100
+++ b/src/Pure/PIDE/xml.scala	Fri Dec 01 20:41:59 2017 +0100
@@ -149,6 +149,8 @@
     private val table =
       Collections.synchronizedMap(new WeakHashMap[Any, WeakReference[Any]](initial_size))
 
+    def size: Int = table.size
+
     private def lookup[A](x: A): Option[A] =
     {
       val ref = table.get(x)