code: function uniq(el, arr){
    arr = arr && arr.join ? arr : [];
    if (!el) return arr.join(' > ');
    if (9 == el.nodeType) return arr.join(' > ');
    if (1 != el.nodeType) return arr.join(' > ');
    arr.unshift(selector(el));
    if (el.id) return arr.join(' > ');
    return uniq(el.parentNode, arr);
  }
docs: Generate unique selector of `el`.
  
  @param {Element} el
  @return {String}
  @api public