Exactly as described, this is a bitmap of C-VLAN PCP values to test with, used only when EncapType is dot1q, since under QinQ the description notes the C-tag's PCP is deliberately set equal to the S-tag's PCP to simplify the software. This QinQ simplification means an operator trying to independently control inner and outer PCP values under double-tagging will find that isn't actually possible on this platform -- only SPcp is settable in that mode, and CPcp is effectively a don't-care that gets overridden to match it. For example, an operator switching a profile from dot1q to QinQ encapsulation would find whatever CPcp bitmap was previously configured no longer has independent effect, since QinQ mode forces it to mirror SPcp instead.