1.    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
    2.               Requirement Levels", BCP 14, RFC 2119, March 1997.
    4.    [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
    5.               Specifications: ABNF", STD 68, RFC 5234, January 2008.
    7.    [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
    8.               Protocol (HTTP/1.1): Message Syntax and Routing",
    9.               RFC 7230, June 2014.
    11.    [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
    12.               Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
    13.               June 2014.
    15.    [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
    16.               Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
    17.               RFC 7234, June 2014.