src/Pure/library.ML

   | is_quasi_letter "'" = true
   | is_quasi_letter ch = is_letter ch;
 
 (*white space: blanks, tabs, newlines, formfeeds*)
 val is_blank : string -> bool =
-  fn " " => true | "\t" => true | "\n" => true | "\^L" => true | _ => false;
+  fn " " => true | "\t" => true | "\n" => true | "\^L" => true | "160" => true
+    | _ => false;
 
 val is_letdig = is_quasi_letter orf is_digit;
 
 (*printable chars*)
 fun is_printable c = ord c > ord " " andalso ord c <= ord "~";