P. Toynbee. Concise Dictionary of Proper Names and Notable Matters in the Works of Dante. Londen, 566: "Addressed (in 1288) by Pope Nicholas IV as 'Rex Sclavorum'; he signed himself (in 1305 or 1307) in a document still extant in the Venetian archives as ' Stephanus Urosch Rex Serbicarum terrarum et maritimarum '. a [Stefano Urosio.] ..."