Section 3.28 Scientific Units
If you are writing about science or engineering, or even if you are not, there is extensive support for scientific units. So, for example, you could author a force in metric units as
<quantity>
<mag>20.7</mag>
<unit prefix="kilo" base="gram" />
<unit base="meter" />
<per base="second" exp="2" />
</quantity>
This would be rendered as 20.7 kg·m⁄s2. More in Section 4.34.
