\newcommand{\etalchar}[1]{$^{#1}$}
\begin{thebibliography}{DDE{\etalchar{+}}11}

\bibitem[Che]{CF}
{Checker Framework} website.
\newblock \url{https://checkerframework.org/}.

\bibitem[DDE{\etalchar{+}}11]{DietlDEMS2011}
Werner Dietl, Stephanie Dietzel, Michael~D. Ernst, K{\i}van{\c{c}} Mu{\c{s}}lu,
  and Todd Schiller.
\newblock Building and using pluggable type-checkers.
\newblock In {\em ICSE 2011, Proceedings of the 33rd International Conference
  on Software Engineering}, pages 681--690, Waikiki, Hawaii, USA, May 2011.

\bibitem[Ern13]{JSR308-webpage-201310}
Michael~D. Ernst.
\newblock {Type Annotations} specification ({JSR} 308).
\newblock \url{https://checkerframework.org/jsr308/}, October 2013.

\bibitem[LBR06]{LeavensBR2006:JML}
Gary~T. Leavens, Albert~L. Baker, and Clyde Ruby.
\newblock Preliminary design of {JML}: A behavioral interface specification
  language for {Java}.
\newblock {\em ACM SIGSOFT Software Engineering Notes}, 31(3), March 2006.

\end{thebibliography}