function validateForm(f) {
  var e1, e2;
  if( !LastButtonClicked) return true;

  if( LastButtonClicked.id == 'btn_submit') {

    if( !(e1 = document.getElementById('keywords'))) return false;
    e1.value = trim(e1.value,'');
    if( e1.value == '' ) {
      alert('No search keywords provided.');
      LastButtonClicked.style.visibility = "visible";
      return false;
    }

  } // End of 'btn_submit'
  return true;
}