code: func attributeNotEqualSelector(key, val string) Selector {
  	key = toLowerASCII(key)
  	return func(n *html.Node) bool {
  		if n.Type != html.ElementNode {
  			return false
  		}
  		for _, a := range n.Attr {
  			if a.Key == key && a.Val == val {
  				return false
  			}
  		}
  		return true
  	}
  }
docs: // attributeNotEqualSelector returns a Selector that matches elements where
  // the attribute named key does not have the value val.