Question: What does a `FeatureSetDownlinkId` value of 0 indicate for a User Equipment (UE: User Equipment) in the context of downlink feature sets as per Radio Resource Control (RRC) protocol specifications?
Option 1: The UE supports the default downlink feature set for all bands.
Option 2: The first downlink feature set in the `featureSetsDownlink` list is selected by the UE.
Option 3: The UE does not support a carrier in this band or band combination.
Option 4: All downlink feature sets are enabled simultaneously for the UE.
Explanation: According to the RRC protocol specifications, a `FeatureSetDownlinkId` of 0 has a specific meaning. It is not associated with an actual downlink feature set but rather indicates that the User Equipment (UE) lacks support for a carrier operating in the specified band or band combination. This distinction is crucial for network configuration and compatibility assessments.