code: function lineplot(data, x, y, opts) {
          var line = d3.svg.line().x(x).y(y).interpolate(xinterp),
              bgline = d3.svg.line().x(x).y(y),
              strokeWidth = _get(opts, "stroke-width", 3),
              color = _get(opts, "stroke", "steelblue");
          el.append("svg:path").attr("d", bgline(data))
                               .style("stroke", "white")
                               .style("stroke-width", 2 * strokeWidth + "px")
                               .style("fill", "none")
                               .attr("class", "bgline");
          el.append("svg:path").attr("d", line(data))
                               .style("stroke", color)
                               .style("stroke-width", strokeWidth + "px")
                               .style("fill", "none");
      }
docs: Plot styles.