function toggle_visibility(evnt, id, expandText, collapseText) {
    var e = document.getElementById(id);
    var src;

    if (evnt != null && evnt.target != null) {
        src = evnt.target;
    }
    else {
        src = event.srcElement;
    }

    if (e.style.display == 'block') {
        e.style.display = 'none';

        if (src.textContent != null) {
            src.textContent = expandText;
        }
        else {
            src.innerText = expandText;
        }

        src.title = expandText;

    }
    else {
        e.style.display = 'block';

        if (src.textContent != null) {
            src.textContent = collapseText;
        }
        else {
            src.innerText = collapseText;
        }

        src.title = collapseText;
    }
}