To draw a mirror image you need to use
two operations: scale and translate.
Output
 |
| SVG version |
Source
<svg width="200" height="100" xmlns="http://www.w3.org/2000/svg" >
<g transform="scale(1,-1) translate(0, -100)">
<text x="0" y="20" font-family="monospace">This is a secret letter.</text>
<text x="0" y="50" font-family="monospace">Can you read it?</text>
</g>
</svg>