Direct-manipulation editors for structured data are increasingly common. While such editors can greatly simplify the creation of structured data, there are few tools to simplify the creation of the editors themselves. This paper presents Citrus, a new programming language and user interface toolkit designed for this purpose. Citrus offers language-level support for constraints, restrictions and change notifications on primitive and aggregate data, mechanisms for automatically creating,

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... and reusing views as data changes, a library of widgets, layouts and behaviors for defining interactive views, and two comprehensive interactive editors as an interface to the language and toolkit itself. Together, these features support the creation of editors for a large class of data and code.