xml is a language for describing markup languages for structured data. A growing number of applications that process xml documents are transformers, i.e., programs that convert documents between xml languages. Unfortunately, the current proposals for transformers are complex general-purpose languages, which will be unappealing as the xml user base broadens and thus decreases in technical sophistication. We have designed and implemented xt3d, a highly declarative xml specification language. It

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... mands little more from users than a knowledge of the expected input and desired output. We illustrate the power of xt3d with several examples, including one reminiscent of polytypic programming that greatly simplifies the import of xml values into general-purpose languages.