Regular Expressions 101

(?sm)applies the following effective flags to the remainder of the pattern: gsm

s modifier: single line. Allows a dot to match line terminators

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Positive Lookahead(?=^((?:Item 1|Item 1a|Item 1b).*?^(?:Item 2|Item 2a|Item 2b)))

^start of line

Group 1((?:Item 1|Item 1a|Item 1b).*?^(?:Item 2|Item 2a|Item 2b))

Non-Capturing Group(?:Item 1|Item 1a|Item 1b)

1st AlternativeItem 1

Item 1the literal text Item 1 (case sensitive)

2nd AlternativeItem 1a

Item 1athe literal text Item 1a (case sensitive)

3rd AlternativeItem 1b

Item 1bthe literal text Item 1b (case sensitive)

.*?any Unicode character, repeated any number of times

^start of line

Non-Capturing Group(?:Item 2|Item 2a|Item 2b)

1st AlternativeItem 2

Item 2the literal text Item 2 (case sensitive)

2nd AlternativeItem 2a

Item 2athe literal text Item 2a (case sensitive)

3rd AlternativeItem 2b

Item 2bthe literal text Item 2b (case sensitive)

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

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Search reference

Regular Expression

(?sm)(?=^((?:Item 1|Item 1a|Item 1b).*?^(?:Item 2|Item 2a|Item 2b)))

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