Using Exception::Class 

• An example from RT::Client::REST

use Exception::Class (
    'RT::Client::REST::OddNumberOfArgumentsException'   => {
        isa         => __PACKAGE__,
        description => "This means that we wanted name/value pairs",
    },

    'RT::Client::REST::InvaildObjectTypeException'   => {
        isa         => __PACKAGE__,
        description => "Invalid object type was specified",
    },

    'RT::Client::REST::MalformedRTResponseException'    => {
        isa         => __PACKAGE__,
        description => "Malformed RT response received from server",
    },
    # ...
);