How proprietary formats have become Microsoft's main tool for lock-in

“A standard that only one implementation fully supports is, from a functional point of view, a proprietary format with a standardisation certificate.”

OOXML got rubber-stamped as an open standard two decades ago, then Microsoft made sure nobody else could implement it fully. The spec is thousands of pages of undocumented behavior and legacy quirks that only Office knows how to render. Your documents are hostages. The certificate is a fig leaf.