1. A method of operating a set of real-world devices that form a real-world ambient environment for a user, comprising: receiving a signal, analysing said signal to produce a real-world description in the form of an instruction set of a markup language, operating said real-world devices to control the real-world ambient environment according to said real-world description, and providing a user interface that allows the user to set limits on the real-world devices that are controlled by the real-world description including setting a maximum level of light provided from a real-world lighting device and a maximum rate of change in light intensity.