^start of string
Character Class[a-zA-Z0-9]* *matches any number of characters from the set below:
a-zone character from a (9710) to z (12210) (case sensitive)
A-Zone character from A (6510) to Z (9010) (case sensitive)
0-9one character from 0 (4810) to 9 (5710)
_the literal _ (9510 / 1378 / 5F16)
?repeats the group contents below at most once:
a_the literal text a_ (case sensitive) .*any character (except for line terminators), repeated any number of times
?repeats the group contents below at most once:
_the literal _ (9510 / 1378 / 5F16)
\d+a digit, repeated at least once
\.the literal . (4610 / 568 / 2E16)
\w+any word character, 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