(function runMailScript(/* GlideRecord */ current, /* TemplatePrinter */ template,
    /* Optional EmailOutbound */ email, /* Optional GlideRecord */ email_action,
    /* Optional GlideRecord */ event) {

    var subject = email.subject;
    var priority = current.priority.getDisplayValue();
    var priorityText = priority.match(/([A-Za-z])\w+/)[0];
    email.setSubject(priorityText + ' ' + subject);

})(current, template, email, email_action, event);