Rick Jelliffe outlined at XML Europe 2002 that there are many stages in the lifecycle of an XML document "When Well-Formed is too much and Validity is too little" and presented a validation process that can be seen as a suite of small validation steps, ranging from documents that are not well-formed to documents that are more than valid.

Making a comparison between the validation processes of SGML and XML, Jelliffe demonstrated that the notion of validation is relative and evolving, and that "well-formed" and "valid" are just two steps in a validation process that can be split into an array of small validation steps.

On one side of the range, documents which are "less than well formed" are common during the process of editing XML documents and, alas, also on the web. However, most of them already have enough structure to be "weakly validated" and having infeasible structures detected at this stage. On the other side, gradual validation may be applied to a document depending on its stage in its lifecycle, using for instance Schematron's phases.

This notion of fuzzy or progressive validation should help users editing XML documents, and is implemented in the Topologi Markup Editor, an innovative XML editor which should be released this quarter.

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