Not sure if this is the right place to mention this, but
In section 3.10 the author states: "An event is an indication of (signifies) an occurrence, not an action". Later the section explains the "why" the events exist and "what" they should be used for.

1. The statement "An event signifies an occurrence, not an action" gives an impression that the specification does not consider event objects dispatched by the user agent as a result of user action as "event". In such a case, an event object IS an indication of an action. An argument can be made to state that such an event object is the result of the occurrence of an activity and hence the statement remains valid. But in the case of synthetic events, a synthetic event can be dispatched as a result of a custom action. In this case, the event is an indication that an action and should remain a valid use of event given that no new activity is started as a consequence of this event being generated.

2. Based on the explanation provided later, perhaps we can modify it as
   "An event signifies the occurrence of an activity, and are not meant to introduce action"

Do you think this change is not required because of the excellent explanation written later? Maybe the statement is good enough and I am missing some point here?