Berlin delivers content to a web server as HTML
The rules will propably look very similar to the ones of the 2D GUI ones, just that the Kit uses HTML instead of taskets/widgets. Some things like D&D drop and maybe menus are not available and alternatives have to be found, but that are minor changes.
If the configurability is restricted for the user, an implementation may create static templates containing the overall structure, which can be merged with the content during productive operation. That way, the run-time overhead is comparable with usual web-applications.