【svg动画】为啥这段代码无效？

Question

<svg xmlns="http://www.w3.org/2000/svg">
    <svg width="500" height="500">
        <rect x="250" y="250" width="50" height="50" fill="#4bc0c8">
        <animateTransform attributeName="transform"
            attributeType="XML"
            type="rotate"
            begin="0s"
            from="0 200 200"
            to="360 400 400"
            dur="10s"
            repeatCount="indefinite"/>
        </rect>
    </svg>
</svg>