diff -r 9efdebe24c65 -r 0ffcad1f6130 src/Pure/PIDE/editor.scala
--- a/src/Pure/PIDE/editor.scala	Mon Mar 01 20:12:09 2021 +0100
+++ b/src/Pure/PIDE/editor.scala	Mon Mar 01 22:22:12 2021 +0100
@@ -27,8 +27,8 @@
   /* overlays */
 
   def node_overlays(name: Document.Node.Name): Document.Node.Overlays
-  def insert_overlay(command: Command, fn: String, args: List[String])
-  def remove_overlay(command: Command, fn: String, args: List[String])
+  def insert_overlay(command: Command, fn: String, args: List[String]): Unit
+  def remove_overlay(command: Command, fn: String, args: List[String]): Unit
 
 
   /* hyperlinks */