// Adapted from work by Yucca Korpela
        // http://www.cs.tut.fi/~jkorpela/forms/combo.html
function activate(field) {
  field.disabled=false;
  if(document.styleSheets)field.style.visibility  = 'visible';
  field.focus(); }
function last_choice(selection) {
  return selection.selectedIndex==selection.length - 1; }
function process_choice(selection,textfield) {
    
  if(last_choice(selection)) {
    activate(textfield); }
  else {
    textfield.disabled = true;
    if(document.styleSheets)textfield.style.visibility  = 'hidden';
    textfield.value = ''; }}
function valid(menu,txt) {
  if(menu.selectedIndex == 0) {
    alert('You must make a selection from the menu');
    return false;}
  if(txt.value == '') {
    if(last_choice(menu)) {
      alert('You need to type your choice into the text box');
      return false; }
    else {
      return true; }}
  else {
    if(!last_choice(menu)) {
      alert('Incompatible selection');
      return false; }
    else {
      return true; }}}
function check_choice(selection, textfield) {
  if(!last_choice(selection)) {
    textfield.blur();
    alert('Please check your menu selection first');
    selection.focus(); }
}