public function performInclusions(&$attr)
    {
        if (!isset($attr[0])) {
            return;
        }
        $merge = $attr[0];
        $seen  = array(); // recursion guard
        // loop through all the inclusions
        for ($i = 0; isset($merge[$i]); $i++) {
            if (isset($seen[$merge[$i]])) {
                continue;
            }
            $seen[$merge[$i]] = true;
            // foreach attribute of the inclusion, copy it over
            if (!isset($this->info[$merge[$i]])) {
                continue;
            }
            foreach ($this->info[$merge[$i]] as $key => $value) {
                if (isset($attr[$key])) {
                    continue;
                } // also catches more inclusions
                $attr[$key] = $value;
            }
            if (isset($this->info[$merge[$i]][0])) {
                // recursion
                $merge = array_merge($merge, $this->info[$merge[$i]][0]);
            }
        }
        unset($attr[0]);
    }