%% You should probably cite rfc7240 instead of this I-D.
@techreport{snell-http-prefer-15,
    number =    {draft-snell-http-prefer-15},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-snell-http-prefer/15/},
    author =    {James M. Snell},
    title =     {{Prefer Header for HTTP}},
    pagetotal = 16,
    year =      2012,
    month =     oct,
    day =       12,
    abstract =  {This specification defines an HTTP header field that can be used by a client to request that certain behaviors be employed by a server while processing a request.},
}