FSI Viewer can be configured by XML files. XML is short for extensible markup language and is pretty much like HTML, syntax-wise. These XML files contain parameters and values which FSI Viewer loads and interpretes on startup. Making use of different XML configuration files lets you have different appearances of FSI Viewer.
Most parameters can also be set in the HTTP Request if needed.

Currently the FSI Viewer, with its add-ons and all the available plugins offers a total of over 400 parameters, allowing you to configure FSI Viewer to your needs and preferences. Further functionality and layout can be implemented with FSI Skin Plus if needed. Please refer to the FSI Viewer Manual for a list of available parameters.