\param len length of returned buffer
\retval !=0 buffer
\retval =0 record could not be rendered
+
+ txml; charset=marc-8
+ xml; charset=utf-8
+ xml; charset=utf-8; base64(/rec/my/text(), txml; charset=marc-8)
*/
YAZ_EXPORT
const char *yaz_record_render(Z_NamePlusRecord *npr, const char *schema,