In HTTP / 1.0 and since , the first line of the HTTP response is called the status line and includes a numeric status code ( such as `` 404 '' ) and a textual reason phrase ( such as `` Not Found '' ) . The way the user agent handles the response primarily depends on the code and secondarily on the other response header fields . Custom status codes can be used since , if the user agent encounters a code it does not recognize , it can use the first digit of the code to determine the general class of the response .

Question: the first line of http request message is called ____
Answer: status line