code: func NSIterateChildren(ctx NSContext, el *etree.Element, handle NSIterHandler) error {
  	ctx, err := ctx.SubContext(el)
  	if err != nil {
  		return err
  	}
  
  	// Iterate the child elements.
  	for _, child := range el.ChildElements() {
  		err = handle(ctx, child)
  		if err != nil {
  			return err
  		}
  	}
  
  	return nil
  }
docs: // NSIterateChildren iterates the children of an element, invoking the passed
  // handler with each direct child of the element, and the context surrounding
  // that child.