diff --git a/src/Pure/PIDE/xml.scala b/src/Pure/PIDE/xml.scala
--- a/src/Pure/PIDE/xml.scala
+++ b/src/Pure/PIDE/xml.scala
@@ -1,434 +1,441 @@
 /*  Title:      Pure/PIDE/xml.scala
     Author:     Makarius
 
 Untyped XML trees and basic data representation.
 */
 
 package isabelle
 
 
 object XML
 {
   /** XML trees **/
 
   /* datatype representation */
 
   type Attribute = Properties.Entry
   type Attributes = Properties.T
 
   sealed abstract class Tree { override def toString: String = string_of_tree(this) }
   type Body = List[Tree]
   case class Elem(markup: Markup, body: Body) extends Tree
   {
+    private lazy val hash: Int = (markup, body).hashCode()
+    override def hashCode(): Int = hash
+
     def name: String = markup.name
 
     def update_attributes(more_attributes: Attributes): Elem =
       if (more_attributes.isEmpty) this
       else Elem(markup.update_properties(more_attributes), body)
 
     def + (att: Attribute): Elem = Elem(markup + att, body)
   }
   case class Text(content: String) extends Tree
+  {
+    private lazy val hash: Int = content.hashCode()
+    override def hashCode(): Int = hash
+  }
 
   def elem(markup: Markup): XML.Elem = XML.Elem(markup, Nil)
   def elem(name: String, body: Body): XML.Elem = XML.Elem(Markup(name, Nil), body)
   def elem(name: String): XML.Elem = XML.Elem(Markup(name, Nil), Nil)
 
   val no_text: Text = Text("")
   val newline: Text = Text("\n")
 
 
   /* name space */
 
   object Namespace
   {
     def apply(prefix: String, target: String): Namespace =
       new Namespace(prefix, target)
   }
 
   final class Namespace private(prefix: String, target: String)
   {
     def apply(name: String): String = prefix + ":" + name
     val attribute: XML.Attribute = ("xmlns:" + prefix, target)
 
     override def toString: String = attribute.toString
   }
 
 
   /* wrapped elements */
 
   val XML_ELEM = "xml_elem"
   val XML_NAME = "xml_name"
   val XML_BODY = "xml_body"
 
   object Wrapped_Elem
   {
     def apply(markup: Markup, body1: Body, body2: Body): XML.Elem =
       XML.Elem(Markup(XML_ELEM, (XML_NAME, markup.name) :: markup.properties),
         XML.Elem(Markup(XML_BODY, Nil), body1) :: body2)
 
     def unapply(tree: Tree): Option[(Markup, Body, Body)] =
       tree match {
         case
           XML.Elem(Markup(XML_ELEM, (XML_NAME, name) :: props),
             XML.Elem(Markup(XML_BODY, Nil), body1) :: body2) =>
           Some(Markup(name, props), body1, body2)
         case _ => None
       }
   }
 
   object Root_Elem
   {
     def apply(body: Body): XML.Elem = XML.Elem(Markup(XML_ELEM, Nil), body)
     def unapply(tree: Tree): Option[Body] =
       tree match {
         case XML.Elem(Markup(XML_ELEM, Nil), body) => Some(body)
         case _ => None
       }
   }
 
 
   /* traverse text */
 
   def traverse_text[A](body: Body)(a: A)(op: (A, String) => A): A =
   {
     def traverse(x: A, t: Tree): A =
       t match {
         case XML.Wrapped_Elem(_, _, ts) => (x /: ts)(traverse)
         case XML.Elem(_, ts) => (x /: ts)(traverse)
         case XML.Text(s) => op(x, s)
       }
     (a /: body)(traverse)
   }
 
   def text_length(body: Body): Int = traverse_text(body)(0) { case (n, s) => n + s.length }
 
 
   /* text content */
 
   def content(body: Body): String =
   {
     val text = new StringBuilder(text_length(body))
     traverse_text(body)(()) { case (_, s) => text.append(s) }
     text.toString
   }
 
   def content(tree: Tree): String = content(List(tree))
 
 
 
   /** string representation **/
 
   val header: String = "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"
 
   def output_char(c: Char, s: StringBuilder)
   {
     c match {
       case '<' => s ++= "&lt;"
       case '>' => s ++= "&gt;"
       case '&' => s ++= "&amp;"
       case '"' => s ++= "&quot;"
       case '\'' => s ++= "&apos;"
       case _ => s += c
     }
   }
 
   def output_string(str: String, s: StringBuilder)
   {
     if (str == null) s ++= str
     else str.iterator.foreach(c => output_char(c, s))
   }
 
   def string_of_body(body: Body): String =
   {
     val s = new StringBuilder
 
     def text(txt: String) { output_string(txt, s) }
     def elem(markup: Markup)
     {
       s ++= markup.name
       for ((a, b) <- markup.properties) {
         s += ' '; s ++= a; s += '='; s += '"'; text(b); s += '"'
       }
     }
     def tree(t: Tree): Unit =
       t match {
         case XML.Elem(markup, Nil) =>
           s += '<'; elem(markup); s ++= "/>"
         case XML.Elem(markup, ts) =>
           s += '<'; elem(markup); s += '>'
           ts.foreach(tree)
           s ++= "</"; s ++= markup.name; s += '>'
         case XML.Text(txt) => text(txt)
       }
     body.foreach(tree)
     s.toString
   }
 
   def string_of_tree(tree: XML.Tree): String = string_of_body(List(tree))
 
 
 
   /** cache **/
 
   object Cache
   {
     def make(
       xz: XZ.Cache = XZ.Cache.make(),
       max_string: Int = isabelle.Cache.default_max_string,
         initial_size: Int = isabelle.Cache.default_initial_size): Cache =
       new Cache(xz, max_string, initial_size)
 
     val none: Cache = make(XZ.Cache.none, max_string = 0)
   }
 
   class Cache private[XML](val xz: XZ.Cache, max_string: Int, initial_size: Int)
     extends isabelle.Cache(max_string, initial_size)
   {
     protected def cache_props(x: Properties.T): Properties.T =
     {
       if (x.isEmpty) x
       else
         lookup(x) match {
           case Some(y) => y
           case None => store(x.map(p => (Library.isolate_substring(p._1).intern, cache_string(p._2))))
         }
     }
 
     protected def cache_markup(x: Markup): Markup =
     {
       lookup(x) match {
         case Some(y) => y
         case None =>
           x match {
             case Markup(name, props) =>
               store(Markup(cache_string(name), cache_props(props)))
           }
       }
     }
 
     protected def cache_tree(x: XML.Tree): XML.Tree =
     {
       lookup(x) match {
         case Some(y) => y
         case None =>
           x match {
             case XML.Elem(markup, body) =>
               store(XML.Elem(cache_markup(markup), cache_body(body)))
             case XML.Text(text) => store(XML.Text(cache_string(text)))
           }
       }
     }
 
     protected def cache_body(x: XML.Body): XML.Body =
     {
       if (x.isEmpty) x
       else
         lookup(x) match {
           case Some(y) => y
           case None => x.map(cache_tree)
         }
     }
 
     // support hash-consing
     def tree0(x: XML.Tree): XML.Tree =
       if (no_cache) x else synchronized { lookup(x) getOrElse store(x) }
 
     // main methods
     def props(x: Properties.T): Properties.T =
       if (no_cache) x else synchronized { cache_props(x) }
     def markup(x: Markup): Markup =
       if (no_cache) x else synchronized { cache_markup(x) }
     def tree(x: XML.Tree): XML.Tree =
       if (no_cache) x else synchronized { cache_tree(x) }
     def body(x: XML.Body): XML.Body =
       if (no_cache) x else synchronized { cache_body(x) }
     def elem(x: XML.Elem): XML.Elem =
       if (no_cache) x else synchronized { cache_tree(x).asInstanceOf[XML.Elem] }
   }
 
 
 
   /** XML as data representation language **/
 
   abstract class Error(s: String) extends Exception(s)
   class XML_Atom(s: String) extends Error(s)
   class XML_Body(body: XML.Body) extends Error("")
 
   object Encode
   {
     type T[A] = A => XML.Body
     type V[A] = PartialFunction[A, (List[String], XML.Body)]
     type P[A] = PartialFunction[A, List[String]]
 
 
     /* atomic values */
 
     def long_atom(i: Long): String = Library.signed_string_of_long(i)
 
     def int_atom(i: Int): String = Library.signed_string_of_int(i)
 
     def bool_atom(b: Boolean): String = if (b) "1" else "0"
 
     def unit_atom(u: Unit) = ""
 
 
     /* structural nodes */
 
     private def node(ts: XML.Body): XML.Tree = XML.Elem(Markup(":", Nil), ts)
 
     private def vector(xs: List[String]): XML.Attributes =
       xs.zipWithIndex.map({ case (x, i) => (int_atom(i), x) })
 
     private def tagged(tag: Int, data: (List[String], XML.Body)): XML.Tree =
       XML.Elem(Markup(int_atom(tag), vector(data._1)), data._2)
 
 
     /* representation of standard types */
 
     val tree: T[XML.Tree] = (t => List(t))
 
     val properties: T[Properties.T] =
       (props => List(XML.Elem(Markup(":", props), Nil)))
 
     val string: T[String] = (s => if (s.isEmpty) Nil else List(XML.Text(s)))
 
     val long: T[Long] = (x => string(long_atom(x)))
 
     val int: T[Int] = (x => string(int_atom(x)))
 
     val bool: T[Boolean] = (x => string(bool_atom(x)))
 
     val unit: T[Unit] = (x => string(unit_atom(x)))
 
     def pair[A, B](f: T[A], g: T[B]): T[(A, B)] =
       (x => List(node(f(x._1)), node(g(x._2))))
 
     def triple[A, B, C](f: T[A], g: T[B], h: T[C]): T[(A, B, C)] =
       (x => List(node(f(x._1)), node(g(x._2)), node(h(x._3))))
 
     def list[A](f: T[A]): T[List[A]] =
       (xs => xs.map((x: A) => node(f(x))))
 
     def option[A](f: T[A]): T[Option[A]] =
     {
       case None => Nil
       case Some(x) => List(node(f(x)))
     }
 
     def variant[A](fs: List[V[A]]): T[A] =
     {
       case x =>
         val (f, tag) = fs.iterator.zipWithIndex.find(p => p._1.isDefinedAt(x)).get
         List(tagged(tag, f(x)))
     }
   }
 
   object Decode
   {
     type T[A] = XML.Body => A
     type V[A] = (List[String], XML.Body) => A
     type P[A] = PartialFunction[List[String], A]
 
 
     /* atomic values */
 
     def long_atom(s: String): Long =
       try { java.lang.Long.parseLong(s) }
       catch { case e: NumberFormatException => throw new XML_Atom(s) }
 
     def int_atom(s: String): Int =
       try { Integer.parseInt(s) }
       catch { case e: NumberFormatException => throw new XML_Atom(s) }
 
     def bool_atom(s: String): Boolean =
       if (s == "1") true
       else if (s == "0") false
       else throw new XML_Atom(s)
 
     def unit_atom(s: String): Unit =
       if (s == "") () else throw new XML_Atom(s)
 
 
     /* structural nodes */
 
     private def node(t: XML.Tree): XML.Body =
       t match {
         case XML.Elem(Markup(":", Nil), ts) => ts
         case _ => throw new XML_Body(List(t))
       }
 
     private def vector(atts: XML.Attributes): List[String] =
       atts.iterator.zipWithIndex.map(
         { case ((a, x), i) => if (int_atom(a) == i) x else throw new XML_Atom(a) }).toList
 
     private def tagged(t: XML.Tree): (Int, (List[String], XML.Body)) =
       t match {
         case XML.Elem(Markup(name, atts), ts) => (int_atom(name), (vector(atts), ts))
         case _ => throw new XML_Body(List(t))
       }
 
 
     /* representation of standard types */
 
     val tree: T[XML.Tree] =
     {
       case List(t) => t
       case ts => throw new XML_Body(ts)
     }
 
     val properties: T[Properties.T] =
     {
       case List(XML.Elem(Markup(":", props), Nil)) => props
       case ts => throw new XML_Body(ts)
     }
 
     val string: T[String] =
     {
       case Nil => ""
       case List(XML.Text(s)) => s
       case ts => throw new XML_Body(ts)
     }
 
     val long: T[Long] = (x => long_atom(string(x)))
 
     val int: T[Int] = (x => int_atom(string(x)))
 
     val bool: T[Boolean] = (x => bool_atom(string(x)))
 
     val unit: T[Unit] = (x => unit_atom(string(x)))
 
     def pair[A, B](f: T[A], g: T[B]): T[(A, B)] =
     {
       case List(t1, t2) => (f(node(t1)), g(node(t2)))
       case ts => throw new XML_Body(ts)
     }
 
     def triple[A, B, C](f: T[A], g: T[B], h: T[C]): T[(A, B, C)] =
     {
       case List(t1, t2, t3) => (f(node(t1)), g(node(t2)), h(node(t3)))
       case ts => throw new XML_Body(ts)
     }
 
     def list[A](f: T[A]): T[List[A]] =
       (ts => ts.map(t => f(node(t))))
 
     def option[A](f: T[A]): T[Option[A]] =
     {
       case Nil => None
       case List(t) => Some(f(node(t)))
       case ts => throw new XML_Body(ts)
     }
 
     def variant[A](fs: List[V[A]]): T[A] =
     {
       case List(t) =>
         val (tag, (xs, ts)) = tagged(t)
         val f =
           try { fs(tag) }
           catch { case _: IndexOutOfBoundsException => throw new XML_Body(List(t)) }
         f(xs, ts)
       case ts => throw new XML_Body(ts)
     }
   }
 }