To cite package ‘vcdExtra’ in publications use:

  Friendly M, Klorfine G (2026). _vcdExtra: 'vcd' Extensions and
  Additions_. R package version 0.9.9,
  <https://github.com/friendly/vcdextra>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {vcdExtra: 'vcd' Extensions and Additions},
    author = {Michael Friendly and Gavin Klorfine},
    year = {2026},
    note = {R package version 0.9.9},
    url = {https://github.com/friendly/vcdextra},
  }