I gather that [r] (trill) was realized as [ɹ] in different dialects of Old English and Middle English, but when [r] was used, was it an allophone?
In other words, did [r] vary predictably with [ɹ] (or maybe the flap [ɾ]) in specific phonetic contexts, e.g.,
word initial? between vowels? when long /rr/? in consonant clusters? word final?
Recommendations on articles/books with more info are also welcome.