Structured specifications in CASL are formed in various familiar ways (union, extension, translation, reduction, etc.) starting from basic specifications; they may also be named, to facilitate reuse. Section 4.1 considers various pragmatic issues affecting the CASL design. Section 4.2 presents the main concepts that underly the semantics of structured specifications. Finally, Section 4.3 provides examples that illustrate the CASL language constructs for use in structured specifications.