has alarmMailsTo => (
    traits => ['ConfigEmail'],    # trait for type "email"
    conf_key => 'ALARM_MAILS_TO'  # associate with a config key
    isa => 'ArrayRef[Str]',
    is => 'rw',
);

##</code><code>##

..
with My::Config;

## some runtime information, eventually for the trait's method
has validDomain => (
    isa => 'Str',
    is => 'rw',
);

has alarmMailsTo => (
    traits => ['ConfigEmail'],
    conf_key => 'ALARM_MAILS_TO'
    attr_valid_domain => 'validDomain'  ## give attr name to trait
    isa => 'ArrayRef[Str]',
    is => 'rw',
);
..

##</code><code>##

..
role My::Config {
    method load() {
        ..
        ## $attr is a Moose::Meta::Attribute
        $attr->parse($self, $configString);
        ..
    }
    ..
}

##</code><code>##

..
role My::Config::ConfigEmail {
    has attr_valid_domain => (
        isa => 'Str',
        is => 'rw',
        required => 1,
    );
    method parse($instance!, $value!) {
        ..
        $instance
            ->meta
            ->find_attribute_by_name($self->attr_valid_domain)
            ->get_value($instance);
        ..
    }
    ..
}