package brr

on_target ~capture ~propagate ~default et f t is an event that reports events of type et transformed by f on target t such that:

• If capture is true the event occurs during the capture phase. Defaults to false.
• If propagate is true the event is propagated. Defaults to true.
• If default is true the default behaviour is performed. Defaults to true.

on_targets is like on_target except the event occurs for the event kind on the given list of targets.

on_el et f el is for_target et f (El.as_target el).

on_els et f els is for_targets et f (List.map El.as_target els).

unit e is ().

stamp v e is v.

instruct ?propagate ?default e defines the propagation and default behaviour of e according to propagate (defaults to true) and default (defaults to true).