Anatomy of a Pro Search Filter

Below is the skeleton of a Pro Search Filter, containing the default properties and methods.

class Pro_search_filter_foo extends Pro_search_filter {

    protected $params;
    protected $fields;
    protected $priority = 5;

    public function filter($entry_ids)
    {
        return $entry_ids;
    }

    public function fixed_order()
    {
        return FALSE;
    }

    public function exclude()
    {
        return NULL;
    }

    public function results($rows)
    {
        return $rows;
    }

}