func myHandler(w rest.ResponseWriter, r *rest.Request) { w.Header().Set("Content-Type", "application/json") w.WriteHeader(http.StatusOK) w.WriteJson(map[string]string{"message": "Hello, world!"}) }In this example, `Header` is used to set the `Content-Type` header to `application/json`. The `WriteHeader` method is then called to send a HTTP 200 status code to the client. Finally, `WriteJson` is called to send a JSON-encoded response back to the client with the message "Hello, world!". Overall, the `github.com.ant0ine.go-json-rest.rest` package provides a convenient and flexible way to build RESTful APIs in Go.