SVG generate partially rounded rectangle path

rrect.js

// based on http://bl.ocks.org/mbostock/3468167

function roundedRect(x, y, width, height, rtl, rtr, rbr, rbl) {
    return "M" + x + "," + y
         + (rtl ? ("v" + rtl
                 + "a" + rtl + "," + rtl + " 0 0 1 " +  rtl + "," + -rtl) : "")
         + "h" + (width  - (rtl ? rtl : 0) - (rtr ? rtr : 0))
         + (rtr ? ("a" + rtr + "," + rtr + " 0 0 1 " +  rtr + "," +  rtr) : "")
         + "v" + (height - (rtr ? rtr : 0) - (rbr ? rbr : 0))
         + (rbr ? ("a" + rbr + "," + rbr + " 0 0 1 " + -rbr + "," +  rbr) : "")
         + "h" + ((rbr ? rbr : 0) + (rbl ? rbl : 0) - width)
         + (rbl ? ("a" + rbl + "," + rbl + " 0 0 1 " + -rbl + "," + -rbl) : "")
         + "v" + ((rbl ? rbl : 0) + (rtl ? rtl : 0) - height)
         + "z";
}