src/Versatile/Search/ProvidesKeyInterface.php
public function withKey($key)
    {
        $keys = func_num_args() > 1 ? func_get_args() : (array)$key;

        foreach ($keys as $key) {
            $this->keys[] = $key;
        }

        return $this;
    }
public function withKey($key)
    {
        $keys = func_num_args() > 1 ? func_get_args() : (array)$key;

        foreach ($keys as $key) {
            $this->keys[] = $key;
        }

        return $this;
    }
Adds a key or many keys (columns) to the result.
Pass an array of keys or just one key or multiple (string) arguments

@param array|string $key
@return self