They are really complex:
https://www.oasis-open.org/2021/06/16/opendocument-v1-3-oasi...
Is the odf counterpart, full on details. The libreoffice implementation:
https://github.com/LibreOffice/core/blob/9667d5e9ebe4a68a772...
I should be done within the week.
[1]: https://github.com/ironcalc/IronCalc