title: XML Parsing Error: no root element found Location (php+Ajax)
body: <p>I want to test php-Ajax with a simple program.I am using html and php file both are stored in same directory (/var/www/html). when I click on button it shows following error in console. 
  XML Parsing Error: no root element found Location. 
  ??</p>
  
  <p><strong>html file</strong></p>
  
  <pre><code>&lt;html&gt;
      &lt;head&gt;
          &lt;meta content="text/html;charset=utf-8" http-equiv="Content-Type"&gt;
          &lt;meta content="utf-8" http-equiv="encoding"&gt;
          &lt;title&gt; Ajax testing &lt;/title&gt;
          &lt;script type="text/javascript"&gt;
              function load(){
                      var xmlhttp = new XMLHttpRequest();
                      xmlhttp.onreadystatechange = function() {
                      if (this.readyState == 4 &amp;&amp; this.status == 200) {
                          document.getElementById("result").innerHTML = this.responseText;
                      }
                  };
                  xmlhttp.open("GET", "simple.php" , true);
                  xmlhttp.send();
              }
          &lt;/script&gt;
      &lt;/head&gt;
      &lt;body&gt;
          &lt;button onclick="load();"&gt;Click here&lt;/button&gt;
          &lt;div id="result"&gt; &lt;/div&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p><strong>php file</strong></p>
  
  <pre><code>&lt;?php 
      echo "Hello";
  ?&gt;
  </code></pre>
  
  <p>what is wrong with this code ? </p>