Type files (*.typ), define a basic element type (string, color, number with default values, limit, enums and graphic user interface).
Dfn files (*.dfn), define a structure composed of basic elements, array of basic element, sub structures, array of sub structures and virtual sub structures.
Form files (*.dfn_name), implement a Dfn file (the name of the Dfn based file is dfn_name.dfn).
