The document is the unit of encapsulation, often corresponding to a disk-file. The syntax allows complex data which has a tree structure to be encapsulated in text streams or documents for transfer. Additional syntax allows full normalisation and recording of more complex datamodels, such as graphs, by making links between different parts of documents or between documents. Many specific XML based formats have been designed. Of immediate interest amongst the general purpose formats are those in the graphics area.
Vector graphics allows proper zooming and crisp linework and lettering.
This complements the image formats like gif, jpeg and png which until now have been the only easy way to present graphics in a web browser, but often lead to fuzzy looking results. There has also been substantial interest in 3-D graphics in the web community. These have been largely focussed on gaming, which means that support for arbitrary geometries at high-precision within large universes is incomplete. Modeling and manipulating data - XML schemas, UML, XSLT XML relieves the applications developer, and to a much lesser extent the user, of some of the burdens of managing data for transfer. Basic parsers for importing XML data are being built in to many software applications packages, and it can be reliably transported using basic web protocols.