src/Pure/PIDE/headless.scala

       }
 
       def purge_edits: List[Document.Edit_Text] =
         make_edits(Text.Edit.removes(0, text))
 
-      def required(required: Boolean): Theory =
+      def set_required(required: Boolean): Theory =
         if (required == node_required) this
         else new Theory(node_name, node_header, text, required)
     }
 
     sealed case class State(

           for {
             node_name <- theories
             theory <- st1.theories.get(node_name)
           }
           yield {
-            val theory1 = theory.required(st1.is_required(node_name))
+            val theory1 = theory.set_required(st1.is_required(node_name))
             val edits = theory1.node_edits(Some(theory))
             (edits, (node_name, theory1))
           }
         (theory_edits.flatMap(_._1), st1.update_theories(theory_edits.map(_._2)))
       }

         val (doc_blobs1, st1) = st.insert_required(id, theories).update_blobs(files)
         val theory_edits =
           for (theory <- loaded_theories)
           yield {
             val node_name = theory.node_name
-            val theory1 = theory.required(st1.is_required(node_name))
+            val theory1 = theory.set_required(st1.is_required(node_name))
             val edits = theory1.node_edits(st1.theories.get(node_name))
             (edits, (node_name, theory1))
           }
         val file_edits =
           for { node_name <- files if doc_blobs1.changed(node_name) }