A question about making detachments in a battle-forged army: Do all of the Faction Keywords need to match, or just one of them? For the Eldar, all flavors of Eldar have the "Aeldari" faction keyword. Does that mean Dark Eldar, Eldar, and Harlequins can be mixed and matched in the same detachment? If so, the Ynnari army rule that you can mix Aeldari units of all stripes seems unnecessary, unless that's just a way to get them Strength from Death.