Or may be both must have length 6?.

Since it looks as it starts working by successively substituting the right hand sides of the definitions the former main regexp 

^((?&expr))((?&expr))\z

[download]
is translated to:

((.)(.))((.)(.))

[download]
which has 6 parenthesis

In reply to Re: Strange behavior of @- and @+ in perl5.10 regexps by casiano
in thread Strange behavior of @- and @+ in perl5.10 regexps by casiano

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