Language-based editing systems have the potential to become a practical, central, and powerful part of every software engineer's toolkit, but progress has been limited by inattention to user-centered design issues. Major usability requirements for such systems include familiar, unrestricted text editing; coherent user interaction with software; rich, dynamic information display; multiple alternative views; uninterrupted service in the presence of ill-formedness, incompleteness, and inconsistency; description-driven support for multiple languages; and extensibility and customizability. Solutions require better understanding of software engineers and their tasks, appropriate design metaphors, new architectural organizations, and design for adaptation and extension.