A long series of Masoretes provided annotations known as Masora ("tradition"), including defining irregular forms, abnormal patterns, and the number of times a form or word was used as margin or foot notes.
The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. Texts and Manuscripts of the Old Testament by Mark R. Norton, Page 175)