To cite package ‘OPCC’ in publications use:

  Li L (2026). _OPCC: Open Postal Code Correspondence_. R package
  version 1.0.1, <https://github.com/lennon-li/opcc>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {OPCC: Open Postal Code Correspondence},
    author = {Lennon Li},
    year = {2026},
    note = {R package version 1.0.1},
    url = {https://github.com/lennon-li/opcc},
  }