Rule 465.2.c.8
If a Unit has one or more Abilities or effects applying to it that demand it be assigned damage in a specific way that is exclusionary, then the assigning player chooses only one of those abilities to apply when assigning damage. Example: Caitlyn, Patrolling with the Backline ability ("I must be assigned combat damage last.") has been given the Tank ability ("I must be assigned combat damage first."). A player is assigning damage to this Caitlyn with Tank and two units with no abilities. That player can’t fulfill both of Caitlyn’s damage requirements, so they may choose to assign damage to Caitlyn first, fulfilling the Tank requirement, or last, fulfilling the Backline requirement. They can’t choose to apply damage to Caitlyn in between the other two units, because that wouldn’t fulfill either requirement.