code: func (cn *ContentNegotiator) getEncoder(req *http.Request) Encoder {
  	var result = cn.DefaultEncoder
  	accept := req.Header.Get("Accept")
  
  	for k, v := range cn.encoderMap {
  		if strings.Contains(accept, k) {
  			result = v
  			break
  		}
  	}
  	return result
  }
docs: // getEncoder parses the Accept header an returns the appropriate encoder to use