Colin P. Masica, The Indo-Aryan Languages, Cambridge University Press, 1993, ISBN 0-521-29944-6.
«... he agreed with Grierson in seeing Rajasthani influence on Pahari and 'Dardic' influence on (or under) the whole Northwestern group + Pahari [...] Sindhi and including 'Lahnda', Dardic, Romany and West Pahari, there has been a tendency to transfer of 'r' from medial clusters to a position after the initial consonant ...»