function showHelpItem(itemToShow) {
    var item = document.getElementById(itemToShow);
    if (item.style.visibility = 'hidden') {
        item.style.visibility = 'visible';
    }
}

function hideHelpItem(itemToHide) {
    var item = document.getElementById(itemToHide);
    if (item.style.visibility = 'visible') {
        item.style.visibility = 'hidden';
    }
}

function changeButtonCaption() {
    var form = document.getElementById("registration_form");
    var chosen_course = form.course.value;

    if ((chosen_course.slice(0,3) == "sbf") || (chosen_course == "sks")) {
        form.materials.disabled = false;
    }
    else {
        form.materials.checked = false;
        form.materials.disabled = true;
    }
    form.submit.value = ((chosen_course == "charter") || (chosen_course == "miles") || (form.materials.checked == true)) ? "Weiter" : "Abschicken";
}