* @param slicer Slicer to use to process history. Can be the same as the
* slicer of the place, as the HISTORIC flag allows distinguishing
* old messages from fresh ones.
- * @param finish_cb Function called after the last message if the history lesson
+ * @param finish_cb Function called after the last message in the history lesson
* is passed through the @a slicer. NULL if not needed.
* @param finish_cb_cls Closure for @a finish_cb.
* @return Handle to abort history lesson, never NULL (multiple lessons