Can players continue to play reactions and start new chains during a showdown after the initial chain resolves, and how does priority work with when I attack/defend triggers?

Ruling: Yes, players can start multiple chains during a showdown. After any chain resolves (including the initial when I attack/defend triggers), the attacker gets focus and can play an action to start a new chain. After that chain resolves, the defender gets focus. This continues back and forth until both players pass focus consecutively, at which point combat damage occurs.

Sequence:

• When I attack/defend triggers go on the chain (attack triggers first, defend triggers on top)
• Controller of topmost item gets priority and can play reactions
• Priority passes back and forth until both players pass consecutively
• Each item on the chain resolves one at a time, with priority checks between each resolution
• After the entire chain resolves, attacker gets focus and can play an action (starting a new chain) or pass
• After that chain resolves, defender gets focus and can play an action or pass
• This continues until both players pass focus consecutively
• Then combat damage occurs and damage is cleared at the end of combat

Nuances:

• The controller of the next item to be resolved gets priority first (not the person who added the last item)
• When I defend triggers resolve before when I attack triggers, so the defender gets priority first if both types of triggers exist
• Damage clears at the end of combat for all units everywhere, not just at the showdown battlefield
• Damage does NOT clear at the end of an open showdown (moving to an uncontrolled battlefield)
• Focus is only used to play actions/reactions (activated abilities), not triggered abilities like when I attack/defend
• After each individual item on a chain resolves, there is a priority check where reactions can be added before the next item resolves