title: How can WriteAttributeString in WriteElementString
body: <p>i need to Write Attribute String in Write Element String if Write Element String contains string values i'am trying this code but it doesn't work </p>
  
  <pre><code>        w.WriteStartElement("W-TIBCPTRs");
          w.WriteElementString("TYPTRT", TYPTRT);
              if (Regex.IsMatch(CLAFCNO, @"^\d+$"))
              {
                  w.WriteElementString("CLAFCNO", CLAFCNO);
              }
              else
              {
                  w.WriteElementString("CLAFCNO", CLAFCNO);
                  w.WriteAttributeString("verifier", "Non");
              }
          w.WriteElementString("NUMCLI", NUMCLI);
          w.WriteElementString("TYPACT", TYPACT);
          w.WriteEndElement();
  </code></pre>
  
  <p>if i have a string value in CLAFCNO this is the result do i need</p>
  
  <pre><code>&lt;W-TIBCPTR&gt;
    &lt;W-TIBCPTRs&gt;
      &lt;TYPTRT&gt;FDR2 R&lt;/TYPTRT&gt;
      &lt;CLAFCNO verifier="NO"&gt;5D1&lt;/CLAFCNO&gt;
      &lt;NUMCLI&gt;0067781&lt;/NUMCLI&gt;
      &lt;TYPACT&gt;D&lt;/TYPACT&gt;
    &lt;/W-TIBCPTRs&gt;
  &lt;/W-TIBCPTR&gt; 
  </code></pre>
  
  <p>if i have a number i need this result</p>
  
  <pre><code>&lt;W-TIBCPTR&gt;
    &lt;W-TIBCPTRs&gt;
      &lt;TYPTRT&gt;FDR2 R&lt;/TYPTRT&gt;
      &lt;CLAFCNO&gt;5D1&lt;/CLAFCNO&gt;
      &lt;NUMCLI&gt;0067781&lt;/NUMCLI&gt;
      &lt;TYPACT&gt;D&lt;/TYPACT&gt;
  
    &lt;/W-TIBCPTRs&gt;
  &lt;/W-TIBCPTR&gt;  
  </code></pre>