src/Pure/PIDE/xml.scala

       XML.Elem(Markup(int_atom(tag), vector(data._1)), data._2)
 
 
     /* representation of standard types */
 
+    val self: T[XML.Body] = identity
+
     val tree: T[XML.Tree] = (t => List(t))
 
     val properties: T[Properties.T] =
       (props => List(XML.Elem(Markup(":", props), Nil)))
 

         case _ => throw new XML_Body(List(t))
       }
 
 
     /* representation of standard types */
+
+    val self: T[XML.Body] = identity
 
     val tree: T[XML.Tree] = {
       case List(t) => t
       case ts => throw new XML_Body(ts)
     }