Wolfram 1971, p. 38: servi Dei et optimates mei ... qui in regno meo sunt ... dux et princeps Francorum. Wolfram, Herwig (1971). "The Shaping of the Early Medieval Principality as a Type of Non-Royal Rulership". Viator. 2: 33–51. doi:10.1484/J.VIATOR.2.301682.
Higgins 1933, p. 209: Sine patrocinio principis Francorum nec populam aecclesiae regere nec presbiteros vel clericos, monachos vel ancillas Dei defendere possum. Higgins, John Seville (1933). "The Ultramontanism of Saint Boniface". Church History. 2 (4): 197–210. doi:10.1017/s0009640700120566.