See my response in Re: What's missing in Perl 5.10. Basically, you currently need to do something horrid like this:

my $re = qr{
             Digits: \s*
             (?:(?<digits>
               (?:(?<digit>\d)
                 (?{ local @d = (@d, $+{digit}) })
               )+
             )(?{ $digits = \@d }))
        }x;
'hello, world, Digits: 123' =~ /$re/ and print "@$digits\n";
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