会呼吸的圆

<svg width="400" height="400">
		<circle cx="200" cy="200" r="50" style="fill:#ff6600">
			<animate attributeName="r" attributeType="XML" from="50" by="80" 
				begin="0s" dur="2s" fill="freeze" 
				repeatCount="indefinite"
				values="50; 80; 50"
			/>
			<animate attributeName="fill-opacity" attributeType="css"  
				begin="0s" dur="2s" fill="freeze" 
				repeatCount="indefinite"
				values="1; 0.6; 1"
			/>
		</circle>
</svg>