-typedef void disorder_eclient_integer_response(void *v, long value);
-/* completion callback with a integer result */
-
-typedef void disorder_eclient_volume_response(void *v, int l, int r);
-/* completion callback with a pair of integer results */
+/** @brief String result completion callback
+ * @param v User data
+ * @param err Error string or NULL on succes
+ * @param value Result or 0
+ *
+ * @p error will be NULL on success. In this case @p value will be the result.
+ *
+ * @p error will be non-NULL on failure. In this case @p value is always 0.
+ */
+typedef void disorder_eclient_integer_response(void *v,
+ const char *err,
+ long value);
+/** @brief Volume completion callback
+ * @param v User data
+ * @param err Error string or NULL on success
+ * @param l Left channel volume
+ * @param r Right channel volume
+ *
+ * @p error will be NULL on success. In this case @p l and @p r will be the
+ * result.
+ *
+ * @p error will be non-NULL on failure. In this case @p l and @p r are always
+ * 0.
+ */
+typedef void disorder_eclient_volume_response(void *v,
+ const char *err,
+ int l, int r);