code: func RegisterHelper(name string, helper interface{}) {
  	helpersMutex.Lock()
  	defer helpersMutex.Unlock()
  
  	if helpers[name] != zero {
  		panic(fmt.Errorf("Helper already registered: %s", name))
  	}
  
  	val := reflect.ValueOf(helper)
  	ensureValidHelper(name, val)
  
  	helpers[name] = val
  }
docs: // RegisterHelper registers a global helper. That helper will be available to all templates.