Utilizing the expression sets in BRE module is a way to execute and confirm samples for determining applicable fees for customers based on complex data entered by the customer. BRE module is a component of Business Rules Engine (BRE), which is a feature of Public Sector Solutions. It can help public sector agencies to create and manage business rules and logic, such as determining fees or eligibility. Expression sets are modules of BRE that can define expressions that can be reused across multiple rules or matrices. Expression sets can also be executed and confirmed with sample data using the Test Expression Set feature in BRE. Reference: https://help.salesforce.com/s/articleView?id=psc_admin_setup_expression_set.htm&type=5&language=en_US