^start of line
\d+a Unicode decimal digit, repeated at least once
\.the literal . (4610 / 568 / 2E16)
.*any Unicode character (except for line terminators), repeated any number of times
Non-Capturing Group(?:\n(?!\d+\.).*)* *repeats the group contents below any number of times:
\na line-feed (newline) character (ASCII 10)
Negative Lookahead(?!\d+\.) \d+a Unicode decimal digit, repeated at least once
\.the literal . (4610 / 568 / 2E16)
.*any Unicode character (except for line terminators), repeated any number of times
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