title: Fill in an existing xml file using PHP
body: <p>i have an existing XML file and i would like to change certain fields in it using PhP.
  For example say i want to change id and pw. Any help on how to open and write on the certain fields?</p>
  
  <pre><code>        &lt;info&gt;
              &lt;contact:info xmlns:contact="urn:ietf:params:xml:ns:contact-1.0" xsi:schemaLocation="urn:ietf:params:xml:ns:contact-1.0
  contact-1.0.xsd"&gt;
                  &lt;contact:id&gt;reg_contact001&lt;/contact:id&gt;
                  &lt;contact:authInfo&gt;
                      &lt;contact:pw&gt;my-password&lt;/contact:pw&gt;
                  &lt;/contact:authInfo&gt;
              &lt;/contact:info&gt;
          &lt;/info&gt; 
  </code></pre>