\ba Unicode word boundary
Itemthe literal text Item (case sensitive) \s+a Unicode whitespace character, repeated at least once
5the literal 5 (5310 / 658 / 3516)
\.the literal . (4610 / 568 / 2E16)
\s*a Unicode whitespace character, repeated any number of times
*?matches any number of characters from the set below:
\wa Unicode word character
\Wany character that is not a Unicode word character
Positive Lookahead(?=\s*(?:Item\s+[89]\.01|SIGNATURES)\b) \s*a Unicode whitespace character, repeated any number of times
Non-Capturing Group(?:Item\s+[89]\.01|SIGNATURES) 1st AlternativeItem\s+[89]\.01 Itemthe literal text Item (case sensitive) \s+a Unicode whitespace character, repeated at least once
8the literal 8 (5610 / 708 / 3816)
9the literal 9 (5710 / 718 / 3916)
\.the literal . (4610 / 568 / 2E16)
2nd AlternativeSIGNATURES SIGNATURESthe literal text SIGNATURES (case sensitive) \ba Unicode word boundary
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