Shadow Models is an incremental transformation framework for MPS. The name is motivated by the realization that many analyses are easier to do on an model whose structure is different from what the user edits. To be able to run such analyses interactively in an IDE, these ``shadows'' of the user-facing model must be maintained in realtime, and incrementality can deliver the needed short response times. Shadow Models is an incremental model transformation engine for MPS. In the paper we motivate the system through example use cases, and outline the transformation framework.

The definition of a projectional editor does not just specify the notation of a language, but also how users interact with the notation. Because of that it is easy to end up with different interaction styles within one and between multiple languages. The resulting inconsistencies have proven to be a major usability problem. To address this problem, we introduce grammar cells, an approach for declaratively specifying textual notations and their interactions for projectional editors. In the paper we motivate the problem, give a formal definition of grammar cells, and define their mapping to low-level editor behaviors. Our evaluation based on project experience shows that grammar cells improve editing experience by providing a consistent and intuitive ``text editor-like'' user experience for textual notations. At the same time they do not limit language composability and the use of non-textual notations, the primary benefits of projectional editors. We have implemented grammar cells for Jetbrains MPS, but they can also be used with other projectional editors.

To be able to build effective DSLs, these DSLs must not just use language concepts that are aligned with their respective domain, but also use notations that correspond closely to established domain notations – and those are often not purely textual or graphical. The underlying language workbench must support these notations, and combining different notations in a single editor must be supported as well in order to support the coherent definitions of systems that use several DSLs. In this paper we provide an overview over the notations supported by JetBrains MPS. MPS is a language workbench that uses a projectional editor, which, by its very nature, can deal with many different notational styles, including text, prose, math tables and graphics. The various supported notations are illustrated with examples from real-world systems.