When an enum value fails to deserialize due to an invalid value, it doesn't include in the error message what the set of possible values are. Doing so could be useful particularly when an enum value is accepted as an argument to a command, as these error messages are directly consumed by users.

https://github.com/10gen/mongo/blob/5a46b791972f54e58b1e6d79eb77e3735c392db1/src/mongo/idl/idl_parser.cpp#L214-L226