has priv_attr => (
    accessor => '_priv_attr',
    isa      => 'Str',
);

##</code><code>##

has _priv_attr => (
    init_arg => 'priv_attr',
    is       => 'rw',
    isa      => 'Str',
);

##</code><code>##

has _priv_attr => (
    is       => 'rw',
    isa      => 'Str',
);

##</code><code>##

has _priv_attr => (
    init_arg => undef,
    is       => 'rw',
    isa      => 'Str',
);

##</code><code>##

1: Can be initialised using ->new( priv_attr => ... )
2: Can be initialised using ->new( priv_attr => ... )
3: Can be initialised using ->new( _priv_attr => ... )
4: Cannot be initialised from outside the class.