How does the CBOR encoding of SIDs apply to YANG features? This draft
references features and the SID draft allows SIDs for them, but I don't
understand how they are used in the encoding (since features don't appear in
the instance data, they are only at the schema level).
YANG features can occur in the data of a YANG module, e.g., yang-library (RFC 8525). Using a SID instead of an identifier for a feature allows a compact representation.
YANG features only show up on the value side.