^start of string
*the literal (3210 / 408 / 2016) , repeated any number of times
?repeats the group contents below at most once:
\d{4}a digit, repeated exactly 4 times
-?optionally matches the literal - (4510 / 558 / 2D16)
\d{2}a digit, repeated exactly 2 times
-?optionally matches the literal - (4510 / 558 / 2D16)
\d{3}a digit, repeated exactly 3 times
-?optionally matches the literal - (4510 / 558 / 2D16)
\d{4}a digit, repeated exactly 4 times
*the literal (3210 / 408 / 2016) , repeated any number of times
$end of string, or before its final line terminator