To cite package ‘declared’ in publications use:

  Dusa A (2024). _declared: Functions for Declared Missing Values_. R
  package version 0.25.1, <https://github.com/dusadrian/declared>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {declared: Functions for Declared Missing Values},
    author = {Adrian Dusa},
    year = {2024},
    note = {R package version 0.25.1},
    url = {https://github.com/dusadrian/declared},
  }