XVCL: a mechanism for handling variants in software product lines Software reuse focused on product lines has emerged as one of the promising ways to increase software productivity and quality. XVCL (XML-based Variant Configuration Language) is a variability mechanism that we developed for handling variants in software product lines. We apply XVCL to develop product line assets (including the domain model, product line architecture and generic components) as a set of x-frames that are capable of accommodating both commonality and variability in a domain. Specific systems, members of a product line, can be constructed by adapting and composing x-frames. In this paper, we illustrate our approach using examples from our product line project on the Computer Aided Dispatch (CAD) domain.