src/Pure/Isar/document_structure.scala

       val (toks, next_context) = ML_Lex.tokenize_line(SML, line, context)
       val level =
         toks.filterNot(_.is_space) match {
           case List(tok) if tok.is_comment =>
             val s = tok.source
-            if (Word.codepoint_iterator(s).exists(c =>
-                  Character.isLetter(c) || Character.isDigit(c)))
+            if (Codepoint.iterator(s).exists(c => Character.isLetter(c) || Character.isDigit(c)))
             {
               if (s.startsWith("(**** ") && s.endsWith(" ****)")) Some(0)
               else if (s.startsWith("(*** ") && s.endsWith(" ***)")) Some(1)
               else if (s.startsWith("(** ") && s.endsWith(" **)")) Some(2)
               else if (s.startsWith("(* ") && s.endsWith(" *)")) Some(3)