^start of string
-?optionally matches the literal - (4510 / 558 / 2D16)
0-9one character from 0 (4810) to 9 (5710)
\d*a digit, repeated any number of times
?repeats the group contents below at most once:
\.the literal . (4610 / 568 / 2E16)
\d+a digit, repeated at least once
$end of string, or before its final line terminator
g modifier: global. Finds all matches instead of stopping after the first