The Fulcrum by Reuben Walker (@thefulcrum.eurosky.social)

A Standard in Name Only: What OOXML Transitional Tells Us About Format Sovereignty - TDF Community Blog When a public administration is told its documents are stored in “an ISO standard format,” the assumption is reasonable: an ISO standard ought to be a clean, implementable specification that any qualified software vendor can support. Standards exist precisely so that nobody is locked to a single supplier. OOXML — ISO/IEC 29500, the format behind Microsoft’s docx, xlsx and pptx files — does not work this way. The standard is split into two conformance classes. Strict is the clean version: a modern document format, free of legacy baggage, that an independent implementer could reasonably support. Transitional is everything else: a vast catalogue of compatibility features, deprecated elements, platform-specific behaviours, and references to undocumented quirks of Microsoft Office versions from the 1990s. The Transitional class exists to ensure that documents converted from the old binary doc, xls and ppt formats can be represented in XML without loss. There is one detail that matters above all others: Microsoft Office has never produced Strict OOXML by default. The option to save in Strict format is available in the installed desktop applications but is absent from the browser-based versions of Microsoft 365 — and Microsoft’s various editions have long differed in which features they https://blog.documentfoundation.org/blog/2026/06/02/a-standard-in-name-only/