MS Office switched to XML tentatively in 2003 and fully in 2007. The latter formats were standardized (Ecma, ISO) into Office Open XML, but even the previous ve

MS Office switched to XML tentatively in 2003 and fully in 2007. The latter formats were standardized (Ecma, ISO) into Office Open XML, but even the previous version were accessible. I don’t remember whether the spec was publicly available, but you could study the output of some valid documents and figure out what went where.