src/Pure/Thy/sessions.scala

--- a/src/Pure/Thy/sessions.scala	Fri Sep 29 22:12:32 2017 +0200
+++ b/src/Pure/Thy/sessions.scala	Fri Sep 29 22:41:19 2017 +0200
@@ -132,6 +132,9 @@
     def loaded_theory_syntax(name: Document.Node.Name): Option[Outer_Syntax] =
       loaded_theory_syntax(name.theory)
 
+    def node_syntax(nodes: Document.Nodes, name: Document.Node.Name): Option[Outer_Syntax] =
+      nodes(name).syntax orElse loaded_theory_syntax(name)
+
     def known_theory(name: String): Option[Document.Node.Name] =
       known.theories.get(name)