lib-cov/jscoverage.js
function jscoverage_findPos(obj) {
  var result = 0;
  do {
    result += obj.offsetTop;
    obj = obj.offsetParent;
  }
  while (obj);
  return result;
}
function jscoverage_findPos(obj) {
  var result = 0;
  do {
    result += obj.offsetTop;
    obj = obj.offsetParent;
  }
  while (obj);
  return result;
}
http://www.quirksmode.org/js/findpos.html