src/Pure/Thy/thy_syntax.ML

   | Token.AltString     => Markup.altstring
   | Token.Verbatim      => Markup.verbatim
   | Token.Space         => Markup.empty
   | Token.Comment       => Markup.comment
   | Token.InternalValue => Markup.empty
-  | Token.Malformed     => Markup.malformed
   | Token.Error _       => Markup.malformed
   | Token.Sync          => Markup.control
   | Token.EOF           => Markup.control;
 
 fun token_markup tok =