According to information provided by Adams and Smith (2019), the method modifDurationUsingMacDuration() is developed to calculate Modified Duration using the Macaulay Duration and Yield-To-Maturity.
References
Adams,J.F. & Smith,D.J.(2019). Understanding Fixed‑Income Risk and Return. In CFA Program Curriculum 2020 Level I Volumes 1-6. (Vol. 5, pp. 237-299). Wiley Professional Development (P&T). ISBN 9781119593577, https://bookshelf.vitalsource.com/books/9781119593577