The format is used for 3D rapid prototyping machines.
See http://en.wikipedia.org/wiki/STL_(file_format) for details in the file format.
BurrTools supports text mode STL as well as binary mode STL file export. The working is again similar to all. You have the base class and a derived class for concrete grid types (e.g. one for bricks, one for spheres...)
The concrete classes do the grid dependend stuff and add lots of triangles to the file