Can you react to 'when I attack' abilities, and what is the timing/sequence for when I attack and when I defend triggers?

Ruling: Yes, you can react to 'when I attack' abilities using reactions. These abilities create a chain.

Sequence:

• When I attack triggers are declared first (so they resolve last in the chain)
• When I defend triggers are declared last (so they resolve first in the chain)
• Then players can add reactions to the chain

Nuances:

• Only effects that use "when" or "at" are triggers that can be reacted to
• Passive effects that use "while" (like Assault) are not triggers and cannot be reacted to