\1 better written as $1
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and use diagnostics; would elaborate...

    (W syntax) Outside of patterns, backreferences live on as variable
+s.
    The use of backslashes is grandfathered on the right-hand side of 
+a
    substitution, but stylistically it's better to use the variable fo
+rm
    because other Perl programmers will expect it, and it works better
+ if
    there are more than 9 backreferences.
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