Which item is not available to be used for QoS classification in Cisco IOS XR?

Outermost header is always used as the single meaningful info source about the QoS per-hop behavior. On MPLS label imposition, the IP prec classification is copied into the outermost EXP bits. On egress of the Service Provider network when the label is popped, the router propagates the EXP bits down into the IP prec or DSCP field (implies IP prec could start out as 5 on ingress and end up as 0 on egress).