^start of line
\d{0,2}a digit, repeated between 0 and 2 times
?repeats the group contents below at most once:
\.the literal . (4610 / 568 / 2E16)
\d{1,3}a digit, repeated between 1 and 3 times
\s?optionally matches any whitespace character
r?optionally matches the literal r (11410 / 1628 / 7216) (case sensitive)
emthe literal text em (case sensitive) $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