Refactorings are behavior-preserving source code transformations that have become integral to modern Integrated Development Environments (IDEs) and code editors, significantly enhancing software development practices. Our goal is to facilitate the creation of custom refactorings and support users in developing their own. To achieve this, we identify the essential building blocks required for creating composite, modular refactorings. We propose a set of abstractions that enable the development of a robust refactoring engine. These abstractions include an initial set of transformations, program primitives, and an API for precondition checking and static analysis necessary to create new refactorings. We demonstrate how standard refactorings can be effectively composed using these building blocks, providing concrete examples to illustrate their application.