diff --git a/include/qapi/error.h b/include/qapi/error.h
index 341b229066..c2115a6a4a 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -230,6 +230,12 @@ void error_prepend(Error **errp, const char *fmt, ...)
 
 /*
  * Append a printf-style human-readable explanation to an existing error.
+ * If the error is later reported to a human user with
+ * error_report_err() or warn_report_err(), the hints will be shown,
+ * too.  If it's reported via QMP, the hints will be ignored.
+ * Intended use is adding helpful hints on the human user interface,
+ * e.g. a list of valid values.  It's not for clarifying a confusing
+ * error message.
  * @errp may be NULL, but not &error_fatal or &error_abort.
  * Trivially the case if you call it only after error_setg() or
  * error_propagate().
@@ -267,11 +273,13 @@ void error_free_or_abort(Error **errp);
 
 /*
  * Convenience function to warn_report() and free @err.
+ * The report includes hints added with error_append_hint().
  */
 void warn_report_err(Error *err);
 
 /*
  * Convenience function to error_report() and free @err.
+ * The report includes hints added with error_append_hint().
  */
 void error_report_err(Error *err);