Key for authors is the device independent markup language, based on familiar standards and incorporating powerful functional abstractions. Additional abstractions are used for device dependent information, such as stylistic specifications and data concerning the physical placement of presentation elements. These abstractions are organised in ways that allow authoring costs to be managed. Definitions can be reused and shared where appropriate, without compromising the ability to provide highly customised presentations where desired.

The adaptation mechanism employs the abstractions together with delivery context, key information about the device and the network in use. The delivery context includes information taken from a comprehensive device repository in addition to information transmitted by the device itself. The authoring tools associated with the products help insulate authors from the need for expert knowledge of the devices in use, while providing information that can be useful to them where necessary. This presentation will describe a number of the fundamental principles on which this particular approach to device independent site authoring is based.