How do you know when a player has focus, and can the player with focus start a chain by activating a reaction?

Ruling: The attacker gains focus first in a showdown and can pass focus, play an action, or play a reaction. You can use reactions when the chain is empty. Both players must pass priority before proceeding to damage.

Sequence:

• The attacker is the first to gain focus in a showdown
• They can pass to give the other player focus, or play an action or reaction
• After that resolves, the other player in the showdown gains focus
• The order of timings is base speed > action > reaction (each has all properties of the one before)
• Both players must pass priority with no actions before proceeding to damage

Nuances:

• It is not possible to go to damage without your opponent having the chance to play cards
• Reactions can be used when the chain is empty