My take on the docs is that '%4.4d' is legal. Maybe not the most straight forward way, but legal. I think I regularly abuse it this way, a mental hangover from the 's' format I think.

Anyway, no matter, '%04d' doesn't numify here either.

Yuck%4.4d

Update: From perldoc -f sprintf:

Perl permits the following universally-known flags
between the "%" and the conversion letter:

   space   prefix positive number with a space
   +       prefix positive number with a plus sign
   -       left-justify within the field
   0       use zeros, not spaces, to right-justify
   #       prefix non-zero octal with "0", non-zero hex with "0x"
   number  minimum field width
   .number "precision": digits after decimal point for
           floating-point, max length for string, minimum length
           for integer
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