A Domain-Specific Modeling Language (DSMLs) describes the concepts and their relationships of a particular domain, in a metamodel. Using a DSML, it is possible to describe a wide range of different models. These models often share a common base and vary on some parts. Current approaches tend to distinguish the variability language from the DSMLs themselves, implying greater learning curve for DSMLs stakeholders and a significant overhead in product line engineering. We propose to consider variability as an independent aspect to be woven into the DSML to introduce variability capabilities. In particular we detail how variability is woven and how to perform product line derivation. We validate our approach through the weaving of variability into two different metamodels: Ecore and SmartAdapter, our aspect model weaver. These results emphasize how new abilities of the language can be provided by this means.