<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg"
     xmlns:xlink="http://www.w3.org/1999/xlink">
<defs>
    <clipPath id="myclip">
        <path transform="scale(.5)" d="M 0 0 l 200 0 l 0 200 l -200 0 Z"/>
    </clipPath>
</defs>
<g  clip-path="url(#myclip)">
<rect x="0" y="0" width="200" height="200" fill="red"/>
<rect x="0" y="0" width="100" height="100" fill="green"/>
</g>
</svg>