PromoTarget: {
    feature: string;
    when?: PromoRule;
} | {
    limit: string;
    when?: PromoRule;
}

{ feature } promotes a feature to servers NOT using it. { limit } (goal must be buy) sells the plan that raises a plan limit, to servers that use it - aim it with when (e.g. hitLimit:<limit> or limitPct:<limit>:80-). It shows only while a dearer buyable plan raises that limit. Copy may use {plan} and {planLimit}.