difference2d
The boolean operator <difference2d> specifies the difference between the first 2d shape contained and the subsequent ones. The result is a new 2d shape .
Example with the 2d difference of a circle and an offset square extruded to create a 3d solid.
<?xml version="1.0" encoding="utf-8"?>
<xcsg version="1.0">
<linear_extrude dz="1">
<difference2d>
<square size="11" center="false"/>
<circle r="5">
<tmatrix>
<trow c0="1" c1="0" c2="0" c3="8"/>
<trow c0="0" c1="1" c2="0" c3="8"/>
<trow c0="0" c1="0" c2="1" c3="0"/>
<trow c0="0" c1="0" c2="0" c3="1"/>
</tmatrix>
</circle>
</difference2d>
</linear_extrude>
</xcsg>