What is the @NaturalId feature in Hibernate 7 and what is @NaturalIdClass?

@Entity
public class Book {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;         // surrogate PK (internal)

    @NaturalId               // business identifier (external)
    @Column(unique=true, nullable=false)
    private String isbn;

    private String title;
}

// Optimised lookup (uses L2 cache):
Book book = session.byNaturalId(Book.class)
    .using("isbn", "978-0-13-468599-1").load();

// @NaturalIdClass: COMPOSITE natural IDs (NEW in Hibernate 7)
public class EmployeeNaturalId {
    String companyCode;
    String employeeNumber;
    // equals() and hashCode() required
}

@Entity
@NaturalIdClass(EmployeeNaturalId.class)  // NEW in Hibernate 7
public class Employee {
    @Id @GeneratedValue private Long id;
    @NaturalId String companyCode;
    @NaturalId String employeeNumber;
    private String name;
}

// Lookup by composite natural ID:
Employee emp = session.byNaturalId(Employee.class)
    .using("companyCode", "ACME")
    .using("employeeNumber", "EMP-001").load();