2) where can I find a complete list of the tg_ variables? I see this list: https://www.postgresql.org/docs/9.4/static/plpgsql- which includes TG_NAME. OLD, NEW, etc but tg_tag and tg_event are not in the list. Are there other variables I can reference?trigger.html
They are listed at the bottom of the page you linked to.
David J.