Regular Expressions 101

Explanation
Pro

^start of line

Non-Capturing Group(?:(IN|THE|BUSH|COM|NET|ALL)\h*,?\h*(?!.*\1))+

+repeats the group contents below at least once:

Group 1(IN|THE|BUSH|COM|NET|ALL)

1st AlternativeIN

INthe literal text IN (case sensitive)

2nd AlternativeTHE

THEthe literal text THE (case sensitive)

3rd AlternativeBUSH

BUSHthe literal text BUSH (case sensitive)

4th AlternativeCOM

COMthe literal text COM (case sensitive)

5th AlternativeNET

NETthe literal text NET (case sensitive)

6th AlternativeALL

ALLthe literal text ALL (case sensitive)

\h*any horizontal whitespace character, repeated any number of times

,?optionally matches the literal , (44₁₀ / 54₈ / 2C₁₆)

\h*any horizontal whitespace character, repeated any number of times

Negative Lookahead(?!.*\1)

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

\1the text saved by group 1

$end of line

Global pattern flags

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

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

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25 tokens

^(?:(IN|THE|BUSH|COM|NET|ALL)\h*,?\h*(?!.*\1))+$

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