[caetus]

<input type="text" id="inp"/>

[JS]
<script>

var inp = document.getElementById('inp');

inp.addEventListener('blur', function (e) {
  e = e.target || e.srcElement;

  if(e.value.substring(0,2).toLowerCase() == 'td') alert('ok');
  else alert('no')
}, false);


</script>

[/JS]