src/Pure/System/options.scala

   private val PREFS_DIR = Path.explode("$ISABELLE_HOME_USER/etc")
   private val PREFS = PREFS_DIR + Path.basic("preferences")
 
   lazy val options_syntax =
     Outer_Syntax.init() + ":" + "=" + "--" +
-      (SECTION, Keyword.THY_HEADING2) + (PUBLIC, Keyword.THY_DECL) + (OPTION, Keyword.THY_DECL)
+      (SECTION, Keyword.HEADING) + (PUBLIC, Keyword.THY_DECL) + (OPTION, Keyword.THY_DECL)
 
   lazy val prefs_syntax = Outer_Syntax.init() + "="
 
   object Parser extends Parse.Parser
   {