Microsoft started using XML-based document file formats in the early 2000s, and adopted Office Open XML in 2007. XML is like HTML but not limited to web-page ma

Microsoft started using XML-based document file formats in the early 2000s, and adopted Office Open XML in 2007. XML is like HTML but not limited to web-page markup. The reason it wasn't always the case was that the .doc format was initially developed before HTML and XML. The first version of Microsoft's .doc format was developed in 1983. HTML was released in around 1991, after being developed through the late 90s, and XML emerged in the late 90s. To be fair, Microsoft was reasonably fast to move to XML-based formats once it was clear XML was becoming an industry standard.