Priority List Item Constructor (internal docblock).
@constructor
@param key {*}
@param value {*}
@param priority {Number}
@param serial {Number}
@private
function PriorityListItem (key, value, priority, serial) {
            var _priority,
                _serial,
                contextName = 'sjl.stdlib.PriorityListItem';
            /**
             * Key name.  Set on construction.
             * @member sjl.stdlib.PriorityListItem#key {String}
             * @readonly
             */
            /**
             * Value name.  Set on construction.
             * @member sjl.stdlib.PriorityListItem#value {*}
             * @readonly
             */
            /**
             * Serial index.
             * @member sjl.stdlib.PriorityListItem#serial {Number}
             * @readonly
             */
            /**
             * Priority.
             * @member sjl.stdlib.PriorityListItem#priority {Number}
             * @readonly
             */
            Object.defineProperties(this, {
                key: {
                    value: key,
                    enumerable: true
                },
                serial: {
                    get: function () {
                        return _serial;
                    },
                    set: function (value) {
                        sjl.throwTypeErrorIfNotOfType(contextName, 'serial', value, Number);
                        _serial = value;
                    },
                    enumerable: true
                },
                value: {
                    value: value,
                    enumerable: true
                },
                priority: {
                    get: function () {
                        return _priority;
                    },
                    set: function (value) {
                        sjl.throwTypeErrorIfNotOfType(contextName, 'priority', value, Number);
                        _priority = value;
                    },
                    enumerable: true
                }
            });
            this.priority = priority;
            this.serial = serial;
        }