public function __construct() {
		parent::__construct();

		$this->add_schema_entry( 'custom_field', array( $this, 'filter_by_custom_field' ) );
		$this->add_schema_entry( 'custom_field_between', array( $this, 'filter_by_custom_field_between' ) );
		$this->add_schema_entry( 'custom_field_less_than', array( $this, 'filter_by_custom_field_less_than' ) );
		$this->add_schema_entry( 'custom_field_greater_than', array( $this, 'filter_by_custom_field_greater_than' ) );
		$this->add_schema_entry( 'geoloc_lat', array( $this, 'filter_by_geoloc_lat' ) );
		$this->add_schema_entry( 'geoloc_lng', array( $this, 'filter_by_geoloc_lng' ) );
		$this->add_schema_entry( 'geoloc', array( $this, 'filter_by_geoloc' ) );
		$this->add_schema_entry( 'has_geoloc', array( $this, 'filter_by_has_geoloc' ) );
		$this->add_schema_entry( 'near', array( $this, 'filter_by_near' ) );
		$this->add_schema_entry( 'series', array( $this, 'filter_by_in_series' ) );
		$this->add_schema_entry( 'in_series', array( $this, 'filter_by_in_series' ) );
		$this->add_schema_entry( 'related_to', array( $this, 'filter_by_related_to' ) );
	}