When Rek'Sai Swarm Queen's attack trigger allows you to play a unit, can you choose to play it to your base instead of the battlefield, or must it be played to the battlefield?

Ruling: When Rek'Sai Swarm Queen's attack trigger allows you to play a unit, you may choose to play it to your base or to any battlefield you control.

Nuances:

• The "may" wording gives you the choice of where to play the unit, not just whether to play it