13. A computer implemented method for generating user interface documents, the method comprising: loading a user interface document into an editor; generating device class specific representations of the user interface document using an adaptation engine, each device class specific representation referring to a respective device class; determining, using a processor of a machine, complexity values of layout components of the device class specific representations by: accessing a library of stored complexity evaluation functions associated with the layout components, each layout component with respect to each device class having a distinct complexity evaluation function in the library, and calculating a complexity value for each of the layout components with respect to each of the respective device class in the device class specific representations using the corresponding distinct complexity evaluation function accessed from the library, the complexity values being numerical values; and aggregating the complexity values of the respective device class specific representations into a single complexity value for each device class.
13. A computer implemented method for generating user interface documents, the method comprising: loading a user interface document into an editor; generating device class specific representations of the user interface document using an adaptation engine, each device class specific representation referring to a respective device class; determining, using a processor of a machine, complexity values of layout components of the device class specific representations by: accessing a library of stored complexity evaluation functions associated with the layout components, each layout component with respect to each device class having a distinct complexity evaluation function in the library, and calculating a complexity value for each of the layout components with respect to each of the respective device class in the device class specific representations using the corresponding distinct complexity evaluation function accessed from the library, the complexity values being numerical values; and aggregating the complexity values of the respective device class specific representations into a single complexity value for each device class. 16. The method of claim 13 , wherein the determining and aggregating operations are replaced by the operations: executing a pre-pagination run with respect to the device class specific representations by using the adaptation engine; and visualizing the result of the pre-pagination run for the respective device classes in a device class dependent page view.