如何在调用.LoadXml()之前检查字符串输入中的有效xml

string xmlString = "<root><child>text</child></root>";
XmlReader reader = XmlReader.Create(new StringReader(xmlString));
XmlDocument doc = new XmlDocument();
doc.Load(reader);

string xmlString = "<root><child>text</child></root>";
XmlDocument doc = new XmlDocument();
doc.LoadXml(xmlString);
doc.Validate(null);

string xmlString = "<root><child>text</child></root>";
XDocument doc = XDocument.Parse(xmlString);

string xmlString = "<root><child>text</child></root>";
string xsdString = "<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema'><xs:element name='root'><xs:complexType><xs:sequence><xs:element name='child' type='xs:string'/></xs:sequence></xs:complexType></xs:element></xs:schema>";
XmlSchemaSet schemaSet = new XmlSchemaSet();
schemaSet.Add("", XmlReader.Create(new StringReader(xsdString)));
XmlReaderSettings settings = new XmlReaderSettings();
settings.Schemas.Add(schemaSet);
settings.ValidationType = ValidationType.Schema;
XmlReader reader = XmlReader.Create(new StringReader(xmlString), settings);
XmlDocument doc = new XmlDocument();
doc.Load(reader);