diff -r 20304512a33b -r c137a9f038a6 src/Pure/PIDE/document.scala
--- a/src/Pure/PIDE/document.scala	Sat Jun 17 20:24:22 2017 +0200
+++ b/src/Pure/PIDE/document.scala	Mon Jun 19 17:28:48 2017 +0200
@@ -498,6 +498,8 @@
     def is_theory: Boolean = node_name.is_theory
     override def toString: String = node_name.toString
 
+    def try_get_text(range: Text.Range): Option[String]
+
     def node_required: Boolean
     def get_blob: Option[Blob]