I found https://odftoolkit.org/conformance/ODFValidator.html which looks to be roughly what I'm looking for at a *technical* level. Unfortunately it points at quite a lot that's not strict ODF compliant. When setting the save format to 1.4 instead of 1.4 Extended in LibreOffice, validation comes out clean, as expected; but I don't see any ready indication of what, if anything, I've done which is lost in the process, so that part of my question remains. (The resulting file is *much* smaller.) #OpenDocument #ODF #LibreOffice