function change_focus(layer) {
    var item;

    if (document.getElementById) {
        item = document.getElementById(layer);
    } else if (document.all) {
        item = document.all[layer];
    } else if (document.layers) {
        item = document.layers[layer];
    }

    item.focus();
}

function toggle_layer(layer) {
    var style;

    if (document.getElementById) {
        style = document.getElementById(layer).style;
    } else if (document.all) {
        style = document.all[layer].style;
    } else if (document.layers) {
        style = document.layers[layer].style;
    }

    style.display = (style.display == '' ? 'block' : '');
}

function hide_layer(layer) {
    var style;

    if (document.getElementById) {
        style = document.getElementById(layer).style;
    } else if (document.all) {
        style = document.all[layer].style;
    } else if (document.layers) {
        style = document.layers[layer].style;
    }

    style.display = 'none';
}

function image_popup(filename) {
    window.open(filename ,'','toolbar=no,status=no,resizable=yes,scrollbars=yes,width=400, height=320');
}