^start of line
{2}matches exactly 2 characters from the set below:
A-Zone character from A (6510) to Z (9010) (case sensitive)
\d{2}a digit, repeated exactly 2 times
the literal (3210 / 408 / 2016)
Non-Capturing Group(?:\d{4} ){3} {3}repeats the group contents below exactly 3 times:
\d{4}a digit, repeated exactly 4 times
the literal (3210 / 408 / 2016)
\d{4}a digit, repeated exactly 4 times
Non-Capturing Group(?: \d\d?)? ?repeats the group contents below at most once:
the literal (3210 / 408 / 2016)
\da digit
\d?optionally matches a digit
$end of line
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string