Regular Expressions 101

^start of string

Group 1((?=(?=.* (\2?(.?))).*\3.*( \2))){500}

{500}repeats the group contents below exactly 500 times:

Positive Lookahead(?=(?=.* (\2?(.?))).*\3.*( \2))

Positive Lookahead(?=.* (\2?(.?)))

.*any character (except for line terminators), repeated any number of times

the literal ↵ (10₁₀ / 12₈ / A₁₆)

Group 2(\2?(.?))

\2?optionally matches the text saved by group 2

Group 3(.?)

.?optionally matches any character (except for line terminators)

.*any character (except for line terminators), repeated any number of times

\3the text saved by group 3

.*any character (except for line terminators), repeated any number of times

Group 4( \2)

the literal ↵ (10₁₀ / 12₈ / A₁₆)

\2the text saved by group 2

.*any character (except for line terminators), repeated any number of times

\4the text saved by group 4

$end of string, or before its final line terminator

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Search reference

Regular Expression

^((?=(?=.*
(\2?(.?))).*\3.*(
\2))){500}.*\4$

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