src/Pure/PIDE/resources.scala

--- a/src/Pure/PIDE/resources.scala	Thu Dec 28 12:26:57 2017 +0100
+++ b/src/Pure/PIDE/resources.scala	Thu Dec 28 12:36:11 2017 +0100
@@ -188,6 +188,9 @@
     else Some(Document.Node.Header(imports.map((_, Position.none))))
   }
 
+  def is_hidden(name: Document.Node.Name): Boolean =
+    !name.is_theory || name.theory == Sessions.root_name
+
 
   /* blobs */