public static function get_sort_options() {
		$sort_options = [];

		$sort_options[__( 'Select', 'papi' )] = null;

		$sort_options[__( 'Name (alphabetically)', 'papi' )] = function ( $a, $b ) {
			// Backwards compatibility with both `post_title` and `title`.
			return strcmp(
				strtolower( isset( $a->post_title ) ? $a->post_title : $a->title ),
				strtolower( isset( $b->post_title ) ? $b->post_title : $b->title )
			);
		};

		$sort_options[__( 'Post created date (ascending)', 'papi' )] = function ( $a, $b ) {
			return strtotime( $a->post_date ) > strtotime( $b->post_date );
		};

		$sort_options[__( 'Post created date (descending)', 'papi' )] = function ( $a, $b ) {
			return strtotime( $a->post_date ) < strtotime( $b->post_date );
		};

		$sort_options[__( 'Post id (ascending)', 'papi' )] = function ( $a, $b ) {
			// Backwards compatibility with both `ID` and `id`.
			return isset( $a->ID ) ? $a->ID > $b->ID : $a->id > $b->id;
		};

		$sort_options[__( 'Post id (descending)', 'papi' )] = function ( $a, $b ) {
			// Backwards compatibility with both `ID` and `id`.
			return isset( $a->ID ) ? $a->ID < $b->ID : $a->id < $b->id;
		};

		$sort_options[__( 'Post order value (ascending)', 'papi' )] = function ( $a, $b ) {
			return $a->menu_order > $b->menu_order;
		};

		$sort_options[__( 'Post order value (descending)', 'papi' )] = function ( $a, $b ) {
			return $a->menu_order < $b->menu_order;
		};

		$sort_options[__( 'Post modified date (ascending)', 'papi' )] = function ( $a, $b ) {
			return strtotime( $a->post_modified ) > strtotime( $b->post_modified );
		};

		$sort_options[__( 'Post modified date (descending)', 'papi' )] = function ( $a, $b ) {
			return strtotime( $a->post_modified ) < strtotime( $b->post_modified );
		};

		return apply_filters( 'papi/property/relationship/sort_options', $sort_options );
	}