function toggle_visibility(id) {
       var e = document.getElementById(id);
       if(e.style.display == 'block')
          e.style.display = 'none';
       else
          e.style.display = 'block';
    }

function hideAllByTag(tagName) {
        var elements = document.getElementsByTagName(tagName);
        var i = 0;
        while (i < elements.length) {
                elements[i].style.display = "none";
                i++;
                }
}