function showElem(idE) {
    if (document.getElementById(idE) != null) {
       var elem = document.getElementById(idE);
       elem.style.visibility='visible';
    }
}
function hideElem(idE) {
    if (document.getElementById(idE) != null) {
       var elem = document.getElementById(idE);
       elem.style.visibility='hidden';
    }
}
function toggleElem(idE) {
    if (document.getElementById(idE) != null) {
       var elem = document.getElementById(idE);
       if (elem.style.visibility!='hidden')
          elem.style.visibility='hidden';
       else
          elem.style.visibility='visible';
    }
}