To cite regDIF in publications use:

Belzak, W. C. M (2021). regDIF: Regularized Differential Item Functioning. version 1.0.0. Duolingo. Pittsburgh, PA. https://github.com/wbelzak/regDIF/

Corresponding BibTeX entry:

  @Manual{,
    title = {regDIF: Regularized Differential Item Functioning},
    author = {William C. M. Belzak},
    organization = {Duolingo},
    address = {Pittsburgh, PA},
    note = {version 1.0.0},
    year = {2021},
    url = {https://github.com/wbelzak/regDIF/},
  }