title: Clear all content in XmlTextWriter and StringWriter
body: <p>I want to clear all of content in XmlTextWriter and StringWriter. Flush() didn't work out.</p>
  
  <p><code>XmlDocument doc = new XmlDocument();</code>
  <code>StringWriter sw = new StringWriter();</code>
  <code>XmlTextWriter xw = new XmlTextWriter(sw);</code></p>
  
  <p><code>xw.WriteStartElement("AddPhoneQual");</code>
  <code>xw.WriteElementString("Type", "B");</code>
  <code>xw.WriteElementString("PhoneNumber", bookingDetails.PassengerList[0].PhoneNumber);</code>
  <code>xw.WriteEndElement();</code> // End AddPhoneQual</p>
  
  <p><code>doc.LoadXml(sw.ToString());</code></p>
  
  <p>Now, i need to clear all of content and start to write in clear xw.</p>
  
  <p><code>xw.Flush();</code>
  <code>sw.Flush();</code></p>
  
  <p>They didn't work.</p>