diff --git a/src/Pure/PIDE/yxml.scala b/src/Pure/PIDE/yxml.scala
--- a/src/Pure/PIDE/yxml.scala
+++ b/src/Pure/PIDE/yxml.scala
@@ -1,155 +1,156 @@
 /*  Title:      Pure/PIDE/yxml.scala
     Author:     Makarius
 
 Efficient text representation of XML trees.  Suitable for direct
 inlining into plain text.
 */
 
 package isabelle
 
 
 import scala.collection.mutable
 
 
 object YXML
 {
   /* chunk markers */
 
   val X = '\u0005'
   val Y = '\u0006'
 
-  val is_X = (c: Char) => c == X
-  val is_Y = (c: Char) => c == Y
+  val is_X: Char => Boolean = _ == X
+  val is_Y: Char => Boolean = _ == Y
 
   val X_string: String = X.toString
   val Y_string: String = Y.toString
   val XY_string: String = X_string + Y_string
   val XYX_string: String = XY_string + X_string
 
   def detect(s: String): Boolean = s.exists(c => c == X || c == Y)
   def detect_elem(s: String): Boolean = s.startsWith(XY_string)
 
 
-  /* string representation */  // FIXME byte array version with pseudo-utf-8 (!?)
+  /* string representation */
 
-  def traversal(string: String => Unit, body: XML.Body): Unit =
+  def traversal(string: String => Unit, body: XML.Body)
   {
     def tree(t: XML.Tree): Unit =
       t match {
         case XML.Elem(Markup(name, atts), ts) =>
           string(XY_string)
           string(name)
           for ((a, x) <- atts) { string(Y_string); string(a); string("="); string(x) }
           string(X_string)
           ts.foreach(tree)
           string(XYX_string)
         case XML.Text(text) => string(text)
       }
     body.foreach(tree)
   }
 
   def string_of_body(body: XML.Body): String =
   {
     val s = new StringBuilder
     traversal(str => s ++= str, body)
     s.toString
   }
 
   def string_of_tree(tree: XML.Tree): String = string_of_body(List(tree))
 
 
   /* parsing */
 
   private def err(msg: String) = error("Malformed YXML: " + msg)
   private def err_attribute() = err("bad attribute")
   private def err_element() = err("bad element")
   private def err_unbalanced(name: String) =
     if (name == "") err("unbalanced element")
     else err("unbalanced element " + quote(name))
 
-  private def parse_attrib(source: CharSequence) = {
+  private def parse_attrib(source: CharSequence): (String, String) =
+  {
     val s = source.toString
     val i = s.indexOf('=')
     if (i <= 0) err_attribute()
     (s.substring(0, i), s.substring(i + 1))
   }
 
 
   def parse_body(source: CharSequence): XML.Body =
   {
     /* stack operations */
 
     def buffer(): mutable.ListBuffer[XML.Tree] = new mutable.ListBuffer[XML.Tree]
     var stack: List[(Markup, mutable.ListBuffer[XML.Tree])] = List((Markup.Empty, buffer()))
 
     def add(x: XML.Tree)
     {
-      (stack: @unchecked) match { case ((_, body) :: _) => body += x }
+      (stack: @unchecked) match { case (_, body) :: _ => body += x }
     }
 
     def push(name: String, atts: XML.Attributes)
     {
       if (name == "") err_element()
       else stack = (Markup(name, atts), buffer()) :: stack
     }
 
     def pop()
     {
       (stack: @unchecked) match {
-        case ((Markup.Empty, _) :: _) => err_unbalanced("")
-        case ((markup, body) :: pending) =>
+        case (Markup.Empty, _) :: _ => err_unbalanced("")
+        case (markup, body) :: pending =>
           stack = pending
           add(XML.Elem(markup, body.toList))
       }
     }
 
 
     /* parse chunks */
 
     for (chunk <- Library.separated_chunks(is_X, source) if chunk.length != 0) {
       if (chunk.length == 1 && chunk.charAt(0) == Y) pop()
       else {
         Library.separated_chunks(is_Y, chunk).toList match {
           case ch :: name :: atts if ch.length == 0 =>
             push(name.toString, atts.map(parse_attrib))
           case txts => for (txt <- txts) add(XML.Text(txt.toString))
         }
       }
     }
     (stack: @unchecked) match {
       case List((Markup.Empty, body)) => body.toList
       case (Markup(name, _), _) :: _ => err_unbalanced(name)
     }
   }
 
   def parse(source: CharSequence): XML.Tree =
     parse_body(source) match {
       case List(result) => result
       case Nil => XML.no_text
       case _ => err("multiple XML trees")
     }
 
   def parse_elem(source: CharSequence): XML.Tree =
     parse_body(source) match {
       case List(elem: XML.Elem) => elem
       case _ => err("single XML element expected")
     }
 
 
   /* failsafe parsing */
 
   private def markup_broken(source: CharSequence) =
     XML.Elem(Markup.Broken, List(XML.Text(source.toString)))
 
   def parse_body_failsafe(source: CharSequence): XML.Body =
   {
     try { parse_body(source) }
     catch { case ERROR(_) => List(markup_broken(source)) }
   }
 
   def parse_failsafe(source: CharSequence): XML.Tree =
   {
     try { parse(source) }
     catch { case ERROR(_) => markup_broken(source) }
   }
 }