In which areas can type constructors be used?

Type constructors are tools in Appian that allow for the creation of complex data types in a flexible way. The correct answer highlights that type constructors can be utilized in expression rules and interfaces.

Expression rules are essential in Appian for establishing reusable logic that can be called across various components. Within these rules, type constructors enable developers to define structured data types, making it easier to manipulate complex data within Appian's environment.

Interfaces, which are used to design user-facing components of applications, also benefit from type constructors. By leveraging these constructors, developers can create dynamic, structured data types tailored to specific user interactions, enhancing the functionality and user experience within the application.

While type constructors can be referenced in other contexts, such as record types and process models, their primary applicability lies within expression rules and interfaces, which is why this answer accurately reflects where they can be effectively used in Appian design.