Regular Expressions 101

Pro

^start of line

Negative Lookahead(?!.*([A-Z]{2}).*\1)

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

Group 1([A-Z]{2})

Character Class[A-Z]{2}

{2}matches exactly 2 characters from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

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

\1the text saved by group 1

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

Global pattern flags

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

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25 tokens

^(?!.*([A-Z]{2}).*\1).*

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