1.    [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
    2.               Extensions (MIME) Part One: Format of Internet Message
    3.               Bodies", RFC 2045, November 1996.
    5.    [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
    6.               Extensions (MIME) Part Two: Media Types", RFC 2046,
    7.               November 1996.
    9.    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
    10.               Requirement Levels", BCP 14, RFC 2119, March 1997.
    12.    [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
    13.               Resource Identifier (URI): Generic Syntax", STD 66,
    14.               RFC 3986, January 2005.
    16.    [RFC4647]  Phillips, A., Ed. and M. Davis, Ed., "Matching of Language
    17.               Tags", BCP 47, RFC 4647, September 2006.
    19.    [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
    20.               Specifications: ABNF", STD 68, RFC 5234, January 2008.
    22.    [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
    23.               Languages", BCP 47, RFC 5646, September 2009.
    25.    [RFC6365]  Hoffman, P. and J. Klensin, "Terminology Used in
    26.               Internationalization in the IETF", BCP 166, RFC 6365,
    27.               September 2011.
    29.    [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
    30.               Protocol (HTTP/1.1): Message Syntax and Routing",
    31.               RFC 7230, June 2014.
    33.    [RFC7232]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
    34.               Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
    35.               June 2014.
    37.    [RFC7233]  Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
    38.               "Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
    39.               RFC 7233, June 2014.
    41.    [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
    42.               Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
    43.               RFC 7234, June 2014.
    45.    [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
    46.               Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014.