+/*
+ * Callback function which will check whether the given change for variable
+ * "item" to "newval" may be applied or not, and possibly apply such change.
+ * When (flag & H_FORCE) is set, it shall not print out any error message and
+ * shall force overwriting of write-once variables.
+.* Must return 0 for approval, 1 for denial.
+ */
+ int (*change_ok)(const ENTRY *__item, const char *newval, enum env_op,
+ int flag);