Dekker 2018, p. 11, "Zaliznjak... calls this 'supra-dialectal Old Russian'... Some attempts have been made to classify Old Novgorodian as a separate Northern branch of the Slavic languages. The mainstream view is still that it is an East Slavic variety, though it has some significant deviations from the 'supra-regional' variety of Old Russian...". Dekker, Simeon (2018). Old Russian Birchbark Letters: A Pragmatic Approach. Brill. ISBN978-90-04-36238-3.