“Th.S.B. Johnston, Codex Hummercensis (Groningen, UB, PEIP 12). An Old Frisian Legal Manuscript in Low Saxon Guise”. BMGN - Low Countries Historical Review, vol. 114, no. 4, Jan. 1999, pp. 589-91, https://doi.org/10.18352/bmgn-lchr.5099.