Array
(
    [PublicationDate.desc] => Array
        (
            [asc] => Array
                (
                    [Books.PublicationDate] => 3
                    [Content.TitleNameFull] => 3
                )

            [desc] => Array
                (
                    [Books.PublicationDate] => 3
                    [Content.TitleNameFull] => 3
                )

            [default] => 3
            [label] => Pub. date - Newest first
        )

    [PublicationDate.asc] => Array
        (
            [asc] => Array
                (
                    [Books.PublicationDate] => 4
                    [Content.TitleNameFull] => 4
                )

            [desc] => Array
                (
                    [Books.PublicationDate] => 4
                    [Content.TitleNameFull] => 4
                )

            [default] => 4
            [label] => Pub. date - Oldest first
        )

)