The MDL Molfile format contains information about the atoms, bonds, connectivity and coordinates of a molecule. A molfile starts with a header block, followed by "connection table". The connection table describes the structural relationships and properties of a collection of atoms. There are two slightly different versions of the format: the regular "V2000" version, and the "V3000" version, which is also known as the extended molfile format. The latter can be identified by a "V3000" version stamp in the header of the file.