/**
 * Toggle visibility of layers
 */
function toggleElement(ddSpan) {
  if (ddSpan != null) {
    if (ddSpan.style.visibility=="hidden" || ddSpan.style.visibility=="") {
      showElement(ddSpan);
    } else {
      hideElement(ddSpan);
    }
  }
}

/**
* show a block-level element
*/
function showElement(ddSpan) {
  ddSpan.style.visibility="visible";
  ddSpan.style.display="inline";
}

/**
* hide a block-level element
*/
function hideElement(ddSpan) {
  ddSpan.style.visibility="hidden";
  ddSpan.style.display="none";
}

/**
 * Toggle visibility of an element, by using right/left arrow button
 */
function toggleVisibility(elementid, buttonid, imgLeft, imgRight) {
  var toggleelt = document.getElementById(elementid);
  var togglebutton = document.getElementById(buttonid);
  if (toggleelt.style.display == "") {
    toggleelt.style.display = "none";
    togglebutton.src = imgRight;
    togglebutton.alt = "show";
  } else {
    toggleelt.style.display = "";
    togglebutton.src = imgLeft;
    togglebutton.alt = "hide";
  }
}