void generateSchemas(MessageSpec message) {
        this.messageFlexibleVersions = message.flexibleVersions();

        // First generate schemas for common structures so that they are
        // available when we generate the inline structures
        for (Iterator<StructSpec> iter = structRegistry.commonStructs(); iter.hasNext(); ) {
            StructSpec struct = iter.next();
            generateSchemas(struct.name(), struct, message.struct().versions());
        }

        // Generate schemas for inline structures
        generateSchemas(message.dataClassName(), message.struct(),
            message.struct().versions());
    }
The versions that implement a KIP-482 flexible schema.
generator/src/main/java/org/apache/kafka/message/SchemaGenerator.java