diff -r 2ad5c46bcd04 -r 123be08eed88 src/Pure/Isar/token.scala
--- a/src/Pure/Isar/token.scala	Thu Jan 24 21:18:30 2013 +0100
+++ b/src/Pure/Isar/token.scala	Fri Jan 25 13:09:34 2013 +0100
@@ -89,6 +89,7 @@
   def is_text: Boolean = is_xname || kind == Token.Kind.VERBATIM
   def is_space: Boolean = kind == Token.Kind.SPACE
   def is_comment: Boolean = kind == Token.Kind.COMMENT
+  def is_improper: Boolean = is_space || is_comment
   def is_proper: Boolean = !is_space && !is_comment
   def is_error: Boolean = kind == Token.Kind.ERROR
   def is_unparsed: Boolean = kind == Token.Kind.UNPARSED