The TextBuffer.ChildAnchorInserted event utilizes this delegate:

Event data is passed via the Gtk.ChildAnchorInsertedArgs parameter.

To attach a Gtk.ChildAnchorInsertedHandler to an event, add the ChildAnchorInsertedHandler instance to the event. The methods referenced by the ChildAnchorInsertedHandler instance are invoked whenever the event is raised, until the ChildAnchorInsertedHandler is removed from the event.