Non-Capturing Group(?:\G|^) \Gstart of current search
\d{1,2}a digit, repeated between 1 and 2 times
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
\Bnot an ASCII word boundary
Positive Lookahead(?=(?:\d{2})*\d{3}(?!\d)) Non-Capturing Group(?:\d{2})* *repeats the group contents below any number of times:
\d{2}a digit, repeated exactly 2 times
\d{3}a digit, repeated exactly 3 times
g modifier: global. Finds all matches instead of stopping after the first
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string