1-9one character from 1 (4910) to 9 (5710)
\d{2}a digit, repeated exactly 2 times
\-the literal - (4510 / 558 / 2D16)
\d{3}a digit, repeated exactly 3 times
\-the literal - (4510 / 558 / 2D16)
\d{4}a digit, repeated exactly 4 times
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