Why can't standalone display when generating xml?

Why can't standalone display when generating xml?

code:

filename = 'ProductMetadata';
docNode = com.mathworks.xml.XMLUtils.createDocument('ProductMetadata');

docRootNode = docNode.getDocumentElement();
publicElement = docNode.createElement('PublicAttribute');
docRootNode.appendChild(publicElement);

SCIDNode = docNode.createElement('SCID');
SCIDNode.appendChild(docNode.createTextNode(sprintf('AD')));
publicElement.appendChild(SCIDNode);

APIDNode = docNode.createElement('APID');
APIDNode.appendChild(docNode.createTextNode(sprintf('APID')));
publicElement.appendChild(APIDNode);

DPIDNode = docNode.createElement('DPID');
DPIDNode.appendChild(docNode.createTextNode(sprintf('XFLX')));
publicElement.appendChild(DPIDNode);

DTTPNode = docNode.createElement('DTTP');
DTTPNode.appendChild(docNode.createTextNode(sprintf('SCI')));
publicElement.appendChild(DTTPNode);

RSFDNode = docNode.createElement('RSFD');
RSFDNode.appendChild(docNode.createTextNode(sprintf('SPEF')));
publicElement.appendChild(RSFDNode);

TSTRNode = docNode.createElement('TSTR');
TSTRNode.appendChild(docNode.createTextNode(sprintf('20211207000001')));
publicElement.appendChild(TSTRNode);

TENDNode = docNode.createElement('TEND');
TENDNode.appendChild(docNode.createTextNode(sprintf('20211207235958')));
publicElement.appendChild(TENDNode);

TaskNONode = docNode.createElement('TaskNO');
TaskNONode.appendChild(docNode.createTextNode(sprintf('0')));
publicElement.appendChild(TaskNONode);

FileNONode = docNode.createElement('FileNO');
FileNONode.appendChild(docNode.createTextNode(sprintf('0221')));
publicElement.appendChild(FileNONode);

ProdLevelNode = docNode.createElement('ProdLevel');
ProdLevelNode.appendChild(docNode.createTextNode(sprintf('L2')));
publicElement.appendChild(ProdLevelNode);

VERNode = docNode.createElement('VER');
VERNode.appendChild(docNode.createTextNode(sprintf('V1')));
publicElement.appendChild(VERNode);

EXTNode = docNode.createElement('EXT');
EXTNode.appendChild(docNode.createTextNode(sprintf('txt')));
publicElement.appendChild(EXTNode);

% PrivateAttribute
privateElement = docNode.createElement('PrivateAttribute');
docRootNode.appendChild(privateElement);

DataProcessingElement = docNode.createElement('DataProcessing');
privateElement.appendChild(DataProcessingElement);

SrcFileNode = docNode.createElement('SrcFile');
a='中国人';
b='北京\n';
SrcFileNode.appendChild(docNode.createTextNode(sprintf(a)));
SrcFileNode.appendChild(docNode.createTextNode(newline));
SrcFileNode.appendChild(docNode.createTextNode(sprintf(b)));

DataProcessingElement.appendChild(SrcFileNode);

ProcessAppNode = docNode.createElement('ProcessApp');
ProcessAppNode.appendChild(docNode.createTextNode(sprintf('XRAY-product-v1.0')));
DataProcessingElement.appendChild(ProcessAppNode);

ProcessStartTimeNode = docNode.createElement('ProcessStartTime');
ProcessStartTimeNode.appendChild(docNode.createTextNode(sprintf('20211208183700')));
DataProcessingElement.appendChild(ProcessStartTimeNode);

ProcessEndTimeNode = docNode.createElement('ProcessEndTime');
ProcessEndTimeNode.appendChild(docNode.createTextNode(sprintf('20211208183900')));
DataProcessingElement.appendChild(ProcessEndTimeNode);

QualityAssessmentElement = docNode.createElement('QualityAssessment');
privateElement.appendChild(QualityAssessmentElement);

IsCompleteNode = docNode.createElement('IsComplete');
IsCompleteNode.appendChild(docNode.createTextNode(sprintf('true')));
QualityAssessmentElement.appendChild(IsCompleteNode);

xmlFileName = [filename,'.xml'];
xmlwrite(xmlFileName,docNode)