function styleHeaderSiblings() {
  if (!document.getElementsByTagName) return false;
  var headers = document.getElementsByTagName("h1");
  for (var i=0; i<headers.length; i++) {
    var elem = getNextElement(headers[i].nextSibling);
    elem.className = "intro";
  }
}

function getNextElement(node) {
  if(node.nodeType == 1) {
	return node;
  }
  if (node.nextSibling) {
    return getNextElement(node.nextSibling);
  }
  return null;
}

window.onload = styleHeaderSiblings;