If there is no anchoring, the regex can match anywhere inside the string. So given the string AAAATGA, the match can work as follow: 
AAAATGA
 XXX
    TGA

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where XXX stands for the letters matched by (\w\w\w). The first A in the string is not matched by anything. Using \G prevents that.

Perl 6 - links to (nearly) everything that is Perl 6.

In reply to Re: \G and regexes by moritz
in thread \G and regexes by 7stud

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