Is there any way to not show the background rectangle?

[calfzhou]

By default, the generated svg will have a white colored polygon as its background and boundary. This rectangle will only be visible when the page is not white. But I'd like to make this background transparent to make the figure looks more comfortable with non-white web page. Is there any way to make it happen?

The default behavior:

But I prefer this:

[calfzhou]

Oh my fault, I could just add an attribute bgcolor=transparent to the graph.