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+In PCRE, following a backreference by _any_ number seems to turn it into an octal value. Why is this?
+
+Eg.
+`(a)\1` <-- Backreference
+`(a)\17` <-- Octal '17'
+`(a)\19` <-- Octal 1, then literal 9
+`(a)\1a` <-- Backreference, then 'a'