What do you with the matches not being the same? 
$_ = 'aaabbb';

while (/((?: a | c? )*)/xg) {
    printf "1: '%s' '%d'\n", $&, pos;  
}
while (/(( a )* | ( c? )?)/xg) {
    printf "2: '%s' '%d'\n", $&, pos;  
}

__END__
1: 'aaa' '3'
1: '' '3'
1: '' '4'
1: '' '5'
1: '' '6'
2: 'aaa' '3'
2: '' '3'
2: '' '4'
2: '' '5'
2: '' '6'

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In reply to Re: ZERO_LENGTH match by Anonymous Monk
in thread ZERO_LENGTH match by sh1tn

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