This interface was rendered based on the LV2 TTL files. Every time you reload this page, proper bundle will be parsed and the layout rendered again.
You can explore some of the pedal funcionality. By moving the knobs, clicking the footswitch and dragging this pedal, you can see how these things will work once the plugin is installed.
To generate a new interface, you can use the wizard. It provides several base layouts that can either be used as final interface or customized as desired. When customizing, you can use the debug button to see what information is available for using in your template.
Full documentation of MOD GUI specifications is available at http://portalmod.com/ns/modgui.