Reverse selector engineering. Get css selector from element. Works with browsers implementing the :nth-of-type selector. Requires mootools selectors.

path.js

// requires mootools selectors

var path = function path(element) {

  if(element.get('id')) {
    return '#' + element.get('id');
  }

  if(element == document.body) {
    return 'body';
  }

  var prev_equal_siblings_length = element.getAllPrevious(element.get('tag')).length;

  var part = element.get('tag') + ':nth-of-type(' + (prev_equal_siblings_length + 1) + ')';

  return path(element.getParent()) + ' > ' + part;

};