11. A data processing system for simulating a structured document as it would appear on different types of media devices, the system comprising: a storage; and a processor operatively coupled to the storage and configured to carry out a process comprising: receiving, via a user interface, a user request to render, in a web browser executing on a first type of media device, a structured document in a layout specific to a second type of media device having a different display requirement than the first type of media device, the second type of media device being selected from a plurality of predefined types of media devices, the structured document being stored in the storage; determining a visual layout of a browser presentation of the structured document in accordance with a style property encoded in a set of presentation semantics associated with and specific to the second type of media device and stored in the storage; and sending the laid out structured document including the style property specific to the second type of media device to the web browser for rendering on the first type of media device.
11. A data processing system for simulating a structured document as it would appear on different types of media devices, the system comprising: a storage; and a processor operatively coupled to the storage and configured to carry out a process comprising: receiving, via a user interface, a user request to render, in a web browser executing on a first type of media device, a structured document in a layout specific to a second type of media device having a different display requirement than the first type of media device, the second type of media device being selected from a plurality of predefined types of media devices, the structured document being stored in the storage; determining a visual layout of a browser presentation of the structured document in accordance with a style property encoded in a set of presentation semantics associated with and specific to the second type of media device and stored in the storage; and sending the laid out structured document including the style property specific to the second type of media device to the web browser for rendering on the first type of media device. 16. The system of claim 11 , wherein the structured document is a web page.