diff -r 7283f41d05ab -r c7693244672e src/Pure/PIDE/document.scala
--- a/src/Pure/PIDE/document.scala	Fri Jan 06 13:27:18 2017 +0100
+++ b/src/Pure/PIDE/document.scala	Fri Jan 06 23:25:18 2017 +0100
@@ -467,6 +467,24 @@
   }
 
 
+  /* model */
+
+  trait Model
+  {
+    /*session*/
+    def session: Session
+    def snapshot(): Snapshot
+
+    /*name*/
+    def node_name: Document.Node.Name
+    def is_theory: Boolean = node_name.is_theory
+    override def toString: String = node_name.toString
+
+    /*content*/
+    def get_blob: Option[Document.Blob]
+  }
+
+
 
   /** global state -- document structure, execution process, editing history **/