(?= ...) is not a "simple grouping", but a look-ahead (ie it looks for the presence of the regex within the group, but doesn't consume any characters).

Use (?: ... ) for just grouping.

(Update: fixed markup)

Perl 6 - second systems done right

In reply to Re: Why does this simple grouping regex not match? by moritz
in thread Why does this simple grouping regex not match? by december

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