var lastField;

function hiddenField(id) {
  if (lastField) {
		lastField.style.visibility = 'hidden';
		lastField.style.display = 'none';
	}
	var hf = document.getElementById('hField-' + id);
	hf.style.visibility = 'visible';
	hf.style.display = 'block';
	lastField = hf;
}