To cite package ‘xfun’ in publications use:

  Xie Y (2024). _xfun: Supporting Functions for Packages Maintained by
  'Yihui Xie'_. R package version 0.49.12,
  <https://github.com/yihui/xfun>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {xfun: Supporting Functions for Packages Maintained by 'Yihui Xie'},
    author = {Yihui Xie},
    year = {2024},
    note = {R package version 0.49.12},
    url = {https://github.com/yihui/xfun},
  }