The terrain for tiles works using the same system as the original STUB engine. There is however a new system to simplify map construction and produce more realistic rendering.
The new system utilises larger textures which are tiled across the map. To enable a tile definition as one of these, you need to add
to the tile definition. The type is an index [0,7] which use matching textures which should be inside the tile folder (with the TILES.TXT definition file). Each type can use 4 different textures, named (e.g. for type 0):
BASE0 NORMAL0 SPEC0 CONTROL0
and are available in the shader in stages 0-3 in the above order. Base tiles edge against other base tiles using the type order to define how (higher types edge out onto lower types). The edging uses a mask in the alpha channel of the BASE texture.
While you can have different sets of 8 base tiles in each tile set, and they can be mixed in a map, there is a limitation that multiple edges from tiles of the same type, but from different sets, cannot meet on the same tile and both edge correctly.