diff -r d6627b50b131 -r c87b7f26e2c7 src/Pure/Syntax/lexicon.ML
--- a/src/Pure/Syntax/lexicon.ML	Mon May 27 20:09:20 2013 +0200
+++ b/src/Pure/Syntax/lexicon.ML	Mon May 27 22:26:08 2013 +0200
@@ -169,7 +169,9 @@
 (* markup *)
 
 fun literal_markup s =
-  if Symbol.is_ascii_identifier s then Markup.literal else Markup.delimiter;
+  if Symbol.is_ascii_identifier s orelse exists Symbol.is_letter (Symbol.explode s)
+  then Markup.literal
+  else Markup.delimiter;
 
 val token_kind_markup =
  fn TFreeSy => Markup.tfree