The Text Encoding Initiative’s Guidelines for electronic text encoding and interchange original aim was to provide exhaustive recommendations for the encoding of literary and linguistic textual materials. In this paper we suggest that the Guidelines are also suitable for the authoring of new material, such as websites and academic papers. With only slight extensions, they can be used to describe the structure and contents of a website, while their modular architecture readily permits customization for multimedia and hyperlinking behaviours. Despite their ‘book-centric’ nature, the Guidelines are sufficiently flexible to cater for information organized in a completely non-book-like manner. We argue that its non-prescriptive nature makes the TEI a good candidate for mapping amongst other possibly more prescriptive XML schemes. As subject-focussed XML-based schemas proliferate, there will be an increasing demand for a non-specific interlingua for the interchange and integration of digital textual data. Our claim is that its extensive coverage, pervasive take-up, rigorous documentation, and well-thought out class mechanism uniquely qualify the TEI for this key role.