src/Tools/jEdit/src/isabelle_sidekick.scala

 {
   override def parser(buffer: Buffer, syntax: Outer_Syntax, data: SideKickParsedData): Boolean =
   {
     val opt_snapshot =
       GUI_Thread.now {
-        Document_Model(buffer) match {
+        PIDE.document_model(buffer) match {
           case Some(model) if model.is_theory => Some(model.snapshot)
           case _ => None
         }
       }
     opt_snapshot match {