function toggle(menuno) {
    if (document.getElementById("submenu" + menuno).style.display == "none") {
        document.getElementById("submenu" + menuno).style.display = "block";
        document.getElementById("mainmenu" + menuno).style.backgroundImage = "url(../Images/collapsetabbg.gif)";
    }
    else if (document.getElementById("submenu" + menuno).style.display == "block") {
        document.getElementById("submenu" + menuno).style.display = "none";
        document.getElementById("mainmenu" + menuno).style.backgroundImage = "url(../Images/expandtabbg.gif)";
    }
    else alert("An error occured in the menu. Contact the web master.");
}