type Filter … // NewAllowKeysFilter returns a Filter that only allows attributes with one of // the provided keys. // // If keys is empty a deny-all filter is returned. func NewAllowKeysFilter(keys ...Key) Filter { … } // NewDenyKeysFilter returns a Filter that only allows attributes // that do not have one of the provided keys. // // If keys is empty an allow-all filter is returned. func NewDenyKeysFilter(keys ...Key) Filter { … }