(?i)applies the following effective flags to the remainder of the pattern: gi i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
\ba Unicode word boundary
\d+a Unicode decimal digit, repeated at least once
?optionally matches the literal (3210 / 408 / 2016)
mthe literal m (10910 / 1558 / 6D16) (case insensitive)
Non-Capturing Group(?:m|illions?)? ?repeats the group contents below at most once:
mthe literal m (10910 / 1558 / 6D16) (case insensitive)
illionthe literal text illion (case insensitive) s?optionally matches the literal s (11510 / 1638 / 7316) (case insensitive)
\ba Unicode word boundary
g modifier: global. Finds all matches instead of stopping after the first