// Exchange images.
// (Browser will scale new image dimensions to the dimensions of the current image.)
function swap(imageName,url) {
  if (document.images) {
    (document.images[imageName].src = url);
  }
}
// Toggle block-element's display status (setting div to display:none collapses its
// space on the page; to hide an element without collapsing the layout, use the visibility
// attribute instead.
function toggleBlockEl(id) {
    if (document.getElementById(id).style.display == 'none') {
        showBlockEl(id);
    } else {
        hide(id);
    }
}
function hide(id) {
    document.getElementById(id).style.display = 'none';
}
function showBlockEl(id) {
    document.getElementById(id).style.display = 'block';
}
function showInlineEl(id) {
    document.getElementById(id).style.display = 'inline';
}