Node in the type inheritance hierarchy. Do not use this class for other purposes as it's definition is subject to change.
|event_tree.g.,
"Finger touches the screen" for touch_down. The event viewer of the
manual shows it. All types defined by the system have a summary.<-id
associated with this node.
|event_node]*, summary=[string]*parent. By creating a new event_node the set
of valid names for the type event_id is extended and event
objects of this new type can be created.
summary describes the new type; see event_node<-summary.
The system defines a node named user for user-defined
event-types.
See also @event_tree, event->initialise
and event->is_a.