^start of line
Group 1(0[1-9]\d|0\d[1-9]|6[0-57-9]\d|6\d[0-57-9]|[1-57-8]\d\d) 0the literal 0 (4810 / 608 / 3016)
1-9one character from 1 (4910) to 9 (5710)
\da digit
0the literal 0 (4810 / 608 / 3016)
\da digit
1-9one character from 1 (4910) to 9 (5710)
3rd Alternative6[0-57-9]\d 6the literal 6 (5410 / 668 / 3616)
0-5one character from 0 (4810) to 5 (5310)
7-9one character from 7 (5510) to 9 (5710)
\da digit
4th Alternative6\d[0-57-9] 6the literal 6 (5410 / 668 / 3616)
\da digit
0-5one character from 0 (4810) to 5 (5310)
7-9one character from 7 (5510) to 9 (5710)
5th Alternative[1-57-8]\d\d 1-5one character from 1 (4910) to 5 (5310)
7-8one character from 7 (5510) to 8 (5610)
\da digit
\da digit
-the literal - (4510 / 558 / 2D16)
\d{2}a digit, repeated exactly 2 times
-the literal - (4510 / 558 / 2D16)
\d{4}a digit, repeated exactly 4 times
$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