When do 'when attacking' effects happen, and can the opponent respond to protect a unit being attacked?

Ruling: 'When attacking' effects are the first thing that enters the chain when you start a showdown. The opponent can only respond with reaction spells, and the attacker has priority to cast their own additional reaction spells first.

Sequence:

• 'When attacking' abilities enter the chain first
• 'When defending' abilities go next
• Reaction spells can be played on top of the chain
• Everything resolves backwards

Nuances:

• The opponent cannot use non-reaction spells since the chain has already started
• The attacker maintains priority to cast additional reaction spells before the opponent