src/Pure/Thy/thy_syntax.ML

   | Token.TypeVar       => Markup.tvar
   | Token.Nat           => Markup.ident
   | Token.String        => Markup.string
   | Token.AltString     => Markup.altstring
   | Token.Verbatim      => Markup.verbatim
-  | Token.Space         => Markup.none
+  | Token.Space         => Markup.empty
   | Token.Comment       => Markup.comment
-  | Token.InternalValue => Markup.none
+  | Token.InternalValue => Markup.empty
   | Token.Malformed     => Markup.malformed
   | Token.Error _       => Markup.malformed
   | Token.Sync          => Markup.control
   | Token.EOF           => Markup.control;