EWL is a language tailored to interactive in-place model transformations on user-selected model elements (unlike ETL which operates in a batch mode). EWL is particularly useful for automating recurring model editing tasks (e.g. refactoring, applying patterns or constructing subtrees consisting of similar elements). EWL is integrated with EMF/GMF and as such, wizards can be executed from within EMF and GMF editors
Chapter 7 of the Epsilon book provides a complete reference of the syntax and semantics of EWL.