A customer extension defines an additional attribute for a requirement, specification, specification folder, chapter, comment, test case, or use case.
Use customer extensions for customizing a requirement or specification for your company. A customer extension added for an object, such as a chapter or specification, automatically appears on forms for that object. For example, the customer extension appears on the Properties page for a requirement.
Customer extensions added in Traceable Requirements Management are also available for CATIA apps.