Thank you for your detailed answer which fits what I had understood from the documentation.
So the #pdresult div is updated with <div id="pdresult1">Your personal details have been saved</div> and I use var pdoptions = { target: '#pdresult', success:function(response) { setTimeout(function(){ $('#pdresult div').fadeOut('slow'); }, 2000); }}; (also tried $("#pdresult1").fadeOut('slow');) but the div pdresult1 doesn't get faded out. What am I missing ? Thanks