diff -r 943dbbbf7ad5 -r 518e28a7c74b src/Pure/PIDE/document.scala
--- a/src/Pure/PIDE/document.scala	Tue Jul 22 22:18:50 2014 +0200
+++ b/src/Pure/PIDE/document.scala	Wed Jul 23 10:02:19 2014 +0200
@@ -167,9 +167,16 @@
     case class Edits[A, B](edits: List[A]) extends Edit[A, B]
     case class Deps[A, B](header: Header) extends Edit[A, B]
     case class Perspective[A, B](required: Boolean, visible: B, overlays: Overlays) extends Edit[A, B]
+
+
+    /* perspective */
+
     type Perspective_Text = Perspective[Text.Edit, Text.Perspective]
     type Perspective_Command = Perspective[Command.Edit, Command.Perspective]
 
+    val empty_perspective_text: Perspective_Text =
+      Perspective(false, Text.Perspective.empty, Overlays.empty)
+
 
     /* commands */