What is ODT?
What LibreOffice, OpenOffice and Google Docs save a document as, and the ISO-standard counterpart to .docx. Inside it is a zip of XML, which is the reason a table drawn in one can be read back out at all. It is a page format first - paragraphs, page breaks, headers, footnotes - so the only part of it that is data is a table someone drew on the page.
What is XML?
Verbose, strict, and still holding up enormous amounts of the world - government feeds, financial messaging, publishing, office documents. JSON took the web from it, but anywhere with schemas and validators and twenty years of history, XML is what's on the wire.