The website version of the tutorial is not ready yet, but the tutorial files in the download package are fully described.

The l3dlevelmodel class is used to load large models, typically representing lightmapped static scene geometry. The geometry was converted from a q3 level. l3dlevelmodel will split geometry into octree on a per face level. It will optimize drawing order depending on material and lightmap useage.

Authors of the level (textures were removed):