code: func Snippet(c context.Context) template.HTML {
  	id := ID(c)
  	if id == "" {
  		return ""
  	}
  	if !rAllowed.MatchString(id) {
  		logging.Errorf(c, "Analytics ID %s does not match UA-\\d+-\\d+", id)
  		return ""
  	}
  	return template.HTML(fmt.Sprintf(`
  <script>
  setTimeout(function() {
  	(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  	(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  	m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  	})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
  
  	ga('create', '%s', 'auto');
  	ga('send', 'pageview');
  }, 0);
  </script>
  `, template.JSEscapeString(id)))
  }
docs: // Snippet returns the html snippet for Google Analytics, including the
  // <script> tag and ID, if ID is set.