my ($re, $bracket, $prefix) = ('');
while (do { ($bracket, $rest, $prefix) = _extract $rest; $bracket }) {
$re .= $self->_commas($prefix) . $self->_brackets($bracket);
}
$re .= $self->_commas($rest);
my ($re, $bracket, $prefix) = ('');
while (do { ($bracket, $rest, $prefix) = _extract $rest; $bracket }) {
$re .= $self->_commas($prefix) . $self->_brackets($bracket);
}
$re .= $self->_commas($rest);