ns = (document.layers) ? 1:0
        ie = (document.all) ? 1:0

function show_expl() {
        if (ns) expl.visibility = "show"
        else if (ie) expl.visibility = "visible"
}

function hide_expl() {
        if (ns) expl.visibility = "hide"
        else if (ie) expl.visibility = "hidden"
}