Find an authoritative statement that MariaDB fully supports the SQL:2016 JSON feature set

A software vendor refuses to support MariaDB on the grounds that they need JSON support, but that "JSON is not inherently included in the basic SQL standard, but it is part of the SQL:2016 standard (ISO/IEC 9075:2016), which MariaDB does not support." (quote from their support). I need to point the vendor's non-technical management to a document that explicitly confirms MariaDB’s compliance with the JSON portion of SQL:2016 standard. I have searched both mariadb.org and mariadb.com and their git repos for the strings "ISO", "9075", "SQL:2016" but I wasn't able to find such a statement, only occasional references.