Write XMLElement nil="true"

I try to set the following attributes in an XML element:<mactive xsi:nil="true"/>.
With the statement XMLElement3.SetAttribute('nil','true') I unfortunately miss "XSI:",

For information I would be grateful


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AL:
XMLDoc := XmlDocument.Create();
XMLDecl := XMLDeclaration.create('1.0', 'UTF-8', 'yes');
XMLDoc.SetDeclaration(XMLDecl);

XMLRootNode := XmlElement.Create('data');
XMLRootNode.Add(XmlAttribute.CreateNamespaceDeclaration('xsi', 'http://www.w3.org/2001/XMLSchema-instance'));
XMLDoc.Add(XMLRootNode);

XMLElement1 := XmlElement.Create('delete');
XMLRootNode.Add(XMLElement1);
XMLElement1 := XmlElement.Create('update');
XMLRootNode.Add(XMLElement1);

XMLElement1 := XmlElement.Create('insert');
XMLRootNode.Add(XMLElement1);

XMLElement2 := XmlElement.Create('muser');
XMLRootNode.Add(XMLElement2);

XMLElement3 := XmlElement.Create('mactive');

XMLElement3.SetAttribute('nil','true'); // xsi: missing
XMLElement2.Add(XMLElement3);

XLM Doc:
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<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<data xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"&gt;
<delete />
<update />
<insert />
<muser>
<mactive nil="true" /> // i would like to have -> <mactive xsi:nil="true"/>
</muser>
</data>