+/** \brief Get a back reference after a successfull match.
+ *
+ * \param n the nfa
+ * \param backref_no the number of the backref to get
+ * \param begin beginning of the matching substring
+ * \param end end of the matching substring
+ *
+ * Returns pointers to the beginning and end of a backref, or null
+ * pointers if one endpoint not met. Those pointers point to the
+ * original buffer that was matched, so the caller will not have to
+ * worry about freeing anything special.
+ *
+ * It is technically possible to create NFAs that meet the start but
+ * not the end of a backref. It is up to the caller to decide how
+ * to handle such a situation.
+ *
+ * \retval 0 OK
+ * \retval 1 no match
+ * \retval 2 no such backref
+ */
+
+int yaz_nfa_get_backref( yaz_nfa *n,
+ int backref_no,
+ yaz_nfa_char **start,
+ yaz_nfa_char **end );