The Camel doesn't fully spell out the use of every built-in function. From perldoc sprintf:

Between the % and the format letter, you may specify a number of additional attributes controlling the interpretation of the format. In order, these are: * format parameter index An explicit format parameter index, such as 2$. By default sprintf will format the next unused argument in the list, but this allows you to take the arguments out of order, e.g.:

printf '%2$d %1$d', 12, 34;      # prints "34 12"
printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"
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