function showFilters() {
  var div = document.getElementById('calfilters');
  var link = document.getElementById('filterlink');
  link.onclick = function () {hideFilters();return false;};
  link.innerHTML = 'Hide filter controls';
  Effect.SlideDown('calfilters');
}

function hideFilters() {
  var div = document.getElementById('calfilters');
  var link = document.getElementById('filterlink');
  link.onclick = function () {showFilters();return false;};
  link.innerHTML = 'Change region or date range';
  Effect.SlideUp('calfilters');
}