function button_onload() {
    document.getElementById('div1').style.visibility = 'visible';
    document.getElementById('div2').style.visibility = 'hidden';
    document.getElementById('div3').style.visibility = 'hidden';
    document.getElementById('extrainfo').style.visibility = 'hidden';
}
function tabclick(id) {
    document.getElementById('div1').style.visibility = 'hidden';
    document.getElementById('div2').style.visibility = 'hidden';
    document.getElementById('div3').style.visibility = 'hidden';
    document.getElementById('div'+id).style.visibility = 'visible';
}
function showExtraInfo() {
    document.getElementById('button').style.visibility = 'hidden';
    document.getElementById('extrainfo').style.visibility = 'visible';
}