src/Pure/Thy/export_theory.scala

     val LOCALE_DEPENDENCY = "locale_dependency"
     val DOCUMENT_HEADING = "document_heading"
     val DOCUMENT_TEXT = "document_text"
     val PROOF_TEXT = "proof_text"
 
-    def export(kind: String): String =
+    def `export`(kind: String): String =
       kind match {
         case Markup.TYPE_NAME => TYPE
         case Markup.CONSTANT => CONST
         case _ => kind
       }