title: Understanding fnServerData in Datatables
body: <p>I am trying to use Datatables in my project. I want to understand the use of "fnServerData" callback option. I have gone through the doc <a href="http://datatables.net/usage/callbacks#fnServerData">Here</a> and have seen following example code -</p>
  
  <pre><code>$(document).ready( function() {
    $('#example').dataTable( {
      "bProcessing": true,
      "bServerSide": true,
      "sAjaxSource": "xhr.php",
      "fnServerData": function ( sSource, aoData, fnCallback, oSettings ) {
        oSettings.jqXHR = $.ajax( {
          "dataType": 'json',
          "type": "POST",
          "url": sSource,
          "data": aoData,
          "success": fnCallback
        } );
      }
    } );
  } );
  </code></pre>
  
  <p>What is "sSource", "aoData" parameters here and how we are supplying values in it? 
  Also, instead of putting a JSP or PHP as a source (sAjaxSource), can we submit a form which will get JSON data dynamically?</p>