VISAT plug-ins implement the {@link org.esa.beam.visat.VisatPlugIn} interface. When VISAT starts up, all classes found in BEAM's extension directory are scanned in order to determine wheather or not they implement this interface. If so, the class is loaded and instance created an the plug-in is registered. After all plugins have been registered, their {@link org.esa.beam.visat.VisatPlugIn#initPlugIn} method is called. A plug-in can then register one or more new commands in VISAT. VISAT then generates either a menu items or a tool bar button or both depending on the command's properties.