LibreOffice has a list of its extension in https://wiki.documentfoundation.org/Development/ODF_Implementer_Notes/List_of_LibreOffice_ODF_Extensions [Such list is requested in section 2.3 of ODF 1.2 part 1]. The ability to put a table into a custom shape has been implemented some time ago. This is done using a <loext:table> element. This is not yet documented in the list. The feature is requested in https://issues.oasis-open.org/browse/OFFICE-3761 but was discussed controversy.
Item found in the mentioned Wikipage as of 2020-09-13.