We present (Microsoft) DialogXML -- a markup language approach to specifying and realising mixed-initiative web dialogs on mobile devices. By capturing the functional structure of the dialog independent of the modalities used to realise it, DialogXML facilitates the implementation of web interfaces that integrate hyperlink and speech modes of interaction. It enables the creation of websites that adapt to the needs of users yet permits the designer fine-grained control over what interactions to support. The framework uses an algorithm based on staging transformations -- an approach that represents dialogs by programs and uses program transformations to simplify them based on user input. Design methodology, implementation details, and two case studies are presented.