public function add($name, $value)
    {
        $this->requireNames();
        $value = $this->normalizeValue($value);
        
        $lower = strtolower($name);
        if(array_key_exists($lower, $this->names)) {
            $name = $this->names[$lower];
            foreach($value as $line) {
                $this->headers[$name][] = $line;
            }
        }else{
            $this->setHeader($name, $value);
        }
    }