It's not referring to the XML formats.. it was a feature of Word specifically which allowed you to embed a user-defined xml schema in your Word document, and us

It's not referring to the XML formats.. it was a feature of Word specifically which allowed you to embed a user-defined xml schema in your Word document, and use XML data that fits the schema in your document. See https://www.zdnet.com/article/custom-xml-the-key-to-patent-suit-over-microsoft-word/ https://www.zdnet.com/article/custom-xml-the-key-to-patent-s... (edit: grammar)