diff --git a/core/XER.hh b/core/XER.hh
index 28f8568f45f3c04002939aeb519ff74e9970eab9..723536146da01297d202dc0e508cdda99cda2826 100644
--- a/core/XER.hh
+++ b/core/XER.hh
@@ -310,7 +310,7 @@ struct XERdescriptor_t
   /** Length of closing tag string (strlen of names[i]) */
   const unsigned short namelens[2];
   /** Various EXER flags */
-  const unsigned long xer_bits;
+  const unsigned long xer_bits; // TODO which types what flags mean what ?
   /** Whitespace handling */
   const XER_whitespace_action whitespace;
   /** value to compare for DEFAULT-FOR-EMPTY */