Hi Delboh,
You could also just draw in Postscript.
^\markup { \postscript #"0.25 setlinewidth 0 0 moveto 0 3 4 3 4 0 curveto stroke" }
You can see the syntax is closely related.
Some may object to that as it removes the possibility of producing SVG output. I have never needed SVG myself, and I use Postscript for a large number of things in my New Complexity School scores.
Andrew