src/Tools/jEdit/src/isabelle.scala

       "isabelle-ml",      // ML source
       "isabelle-markup",  // SideKick markup tree
       "isabelle-news",    // NEWS
       "isabelle-options", // etc/options
       "isabelle-output",  // pretty text area output
-      "isabelle-root")    // session ROOT
+      "isabelle-root",    // session ROOT
+      "sml")              // Standard ML (not Isabelle/ML)
 
   private lazy val ml_syntax: Outer_Syntax =
     Outer_Syntax.init().no_tokens.
       set_language_context(Completion.Language_Context.ML_outer)