When adding new classes to `ServiceClassType`, ensure they adhere to the
following guidelines:

- **Local Standards**: The classes should represent the local standard of service classes for the intended mode of transport in the target market.
- **Hardware-Focused**: They should represent the physical attributes and amenities of the vehicle (the "hardware") rather than a partner's specific pricing structure or fare conditions (e.g. refundability, flexibility).
- **Reusability**: Different partners should be able to use the same classes when providing prices for the same type of vehicle. This avoids proliferation of partner-specific enums and ensures consistency.

### Proto Definition

```protobuf
// Attributes characterizing the amenities and ride comfort of a journey on a
// vehicle.
export message ServiceClass {
  // A high level enum describing the service class type.
  enum ServiceClassType {
    // Global service classes
    FIRST_CLASS = 1;
    SECOND_CLASS = 2;

    // Only a single service class is offered by the operator. The service class
    // may not even have a name because there is no distinction to be made.
    SINGLE_CLASS = 3;
    BUSINESS_CLASS = 4;

    // Additional global or per-market service classes can be added.  Please
    // reach out to the Google Transport team if additional service classes are
    // needed for your use case.

    // Japan specific train ticket classes
    NON_RESERVED_SECOND_CLASS = 201;
    RESERVED_SECOND_CLASS = 202;
    RESERVED_GREEN_CAR_CLASS = 203;
    RESERVED_GRAN_CLASS = 204;

    // Brazil specific service classes.
    CONVENCIONAL = 205;
    EXECUTIVO = 206;
    SEMILEITO = 207;
    LEITO = 208;
    CAMA = 209;

    // Bus specific service classes (commonly used in India).
    // Air-conditioned sleeper class.
    AC_SLEEPER_CLASS = 301;

    // Air-conditioned seater class.
    AC_SEATER_CLASS = 302;

    // Air-conditioned semi-sleeper class.
    AC_SEMI_SLEEPER_CLASS = 303;

    // Air-conditioned sleeper and seater class.
    AC_SLEEPER_SEATER_CLASS = 304;

    // Non-air-conditioned sleeper class.
    NON_AC_SLEEPER_CLASS = 305;

    // Non-air-conditioned seater class.
    NON_AC_SEATER_CLASS = 306;

    // Non-air-conditioned semi-sleeper class.
    NON_AC_SEMI_SLEEPER_CLASS = 307;

    // Non-air-conditioned sleeper and seater class.
    NON_AC_SLEEPER_SEATER_CLASS = 308;
  }

  ServiceClassType type = 1 [features.field_presence = IMPLICIT];
}
```

> [!NOTE]
> **Note:** when using the recommended [protocol buffer libraries](https://github.com/protocolbuffers/protobuf) add a value for `SERVICE_CLASS_TYPE_UNSPECIFIED = 0;` in the `ServiceClass.ServiceClassType` enum.

### JSON Sample

```json
{
  "type": "FIRST_CLASS"
}
```