<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg">
    <marker id="marker" viewBox="0 0 100 100" refX="50" refY="50" markerUnits="strokeWidth" markerWidth="50" markerHeight="50" orient="auto">
        <rect fill="red" x="-50" y="-50" width="200" height="200" />
        <rect x="0" y="0" width="100" height="100" fill="green"/>
    </marker>
    <rect width="25" height="25" />
    <path d="M 100 100 L 100 100 " fill="none" stroke="none" stroke-width="3" marker-start="url(#marker)"/>
    <text x="30" y="20"> There should be a 150x150 green rect at 25x25</text>
</svg>