code: func (c *FormatCheckerChain) Add(name string, f FormatChecker) *FormatCheckerChain {
  	lock.Lock()
  	c.formatters[name] = f
  	lock.Unlock()
  
  	return c
  }
docs: // Add adds a FormatChecker to the FormatCheckerChain
  // The name used will be the value used for the format key in your json schema