".docx is a bad example, because it was standardized" This is not 100% correct. A large part of the format is standardized in ECMA-376 and ISO/IEC 29500, but

".docx is a bad example, because it was standardized" This is not 100% correct. A large part of the format is standardized in ECMA-376 and ISO/IEC 29500, but many details are implementation-dependent. Many of those details are covered under other specifications like [MS-DOCX] that are covered by a covenant not to sue, but other details are not covered and are therefore in murky legal territory. [MS-DOCX] https://docs.microsoft.com/en-us/openspecs/office_standards/ms-docx/b839fe1f-e1ca-4fa6-8c26-5954d0abbccd https://docs.microsoft.com/en-us/openspecs/office_standards/...