If the result of TO-EXPR is not a string, it is converted to one using
`prin1-to-string' with the NOESCAPE argument (which see).
-For convenience, when entering TO-EXPR interactively, you can use `\\&' or
-`\\0' to stand for whatever matched the whole of REGEXP, and `\\N' (where
+For convenience, when entering TO-EXPR interactively, you can use `\\&'
+to stand for whatever matched the whole of REGEXP, and `\\N' (where
N is a digit) to stand for whatever matched the Nth `\\(...\\)' (1-based)
in REGEXP.