function traverseDOM(start){
  var cc = function(){return scanNode(start, stop);};
  function stop(){
    cc = stop;
    throw StopIteration;
  }
  function yield(value, c){
    cc = c;
    return value;
  }

  function scanNode(node, c){
    if (node.nextSibling)
      var nextc = function(){return scanNode(node.nextSibling, c);};
    else
      var nextc = c;

    if (/* node is proper span element */)
      return yield(node.firstChild.nodeValue, nextc);
    else if (/* node is proper br element */)
      return yield("\n", nextc);
    else
      /* flatten node, yield its textual content */;
  }

  return {next: function(){return cc();}};
}