Why can't an arc be drawn via PATH?

Question

HTML

I'm trying to draw an arc using path
The line is visible, but the arc is not.

<?xml version="1.0" encoding="utf-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="1000mm" height="1000mm">
    <line x1="0mm" y1="100mm" x2="15mm" y2="100mm" style="stroke: #FF0000" />
    <path d="M 230mm,100mm A 20mm, 20mm, 0, 0, 0, 270mm,100mm" style="stroke: #FF0000" />
</svg>

If you try to specify pixels in the path as coordinates, it renders. But what you need is millimeters ...

Answer 1

Remove extra commas and units

<path xmlns="http://www.w3.org/2000/svg" d="M230,100 A 20,20 0 0 0 270 100" style="stroke: #FF0000;stroke-width: 5px;fill: red;"/>