%% You should probably cite draft-ietf-calext-ical-tasks instead of this I-D.
@techreport{apthorp-ical-tasks-00,
    number =    {draft-apthorp-ical-tasks-00},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-apthorp-ical-tasks/00/},
    author =    {Adrian Apthorp and Cyrus Daboo and Mike Douglass},
    title =     {{Task Extensions to iCalendar}},
    pagetotal = 27,
    year =      2015,
    month =     jan,
    day =       4,
    abstract =  {This document defines extensions to the Internet Calendaring and Scheduling Core Object Specification (iCalendar) to provide improved status tracking, scheduling and specification of tasks.},
}