\d+a digit, repeated at least once
\s*any whitespace character, repeated any number of times
\.the literal . (4610 / 568 / 2E16)
\s*any whitespace character, repeated any number of times
Group 1((?:.+(?:\r\n?|\n))*?(?=[aA]\))) Non-Capturing Group(?:.+(?:\r\n?|\n))*? *?repeats the group contents below any number of times:
.+any character (except for line terminators), repeated at least once
Non-Capturing Group(?:\r\n?|\n) \ra carriage return (ASCII 13)
\n?optionally matches a line-feed (newline) character (ASCII 10)
\na line-feed (newline) character (ASCII 10)
Positive Lookahead(?=[aA]\)) athe literal a (9710 / 1418 / 6116) (case sensitive)
Athe literal A (6510 / 1018 / 4116) (case sensitive)
\)the literal ) (4110 / 518 / 2916)
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