code: function selector(el){
    var classname = trim(el.className.baseVal ? el.className.baseVal : el.className);
    var i = el.parentNode && 9 == el.parentNode.nodeType ? -1 : index(el);
  
    return el.tagName.toLowerCase()
      + (el.id ? '#' + el.id : '')
      + (classname ? classname.replace(/^| +/g, '.') : '')
      + (~i ? ':nth-child(' + (i + 1) + ')' : '');
  }
docs: Generate a selector of the given `el`.
  
  @param {Element} el
  @return {String}
  @api private