text: import "arc";
  import "diagonal";
  import "svg";
  
  d3.svg.diagonal.radial = function() {
    var diagonal = d3.svg.diagonal(),
        projection = d3_svg_diagonalProjection,
        projection_ = diagonal.projection;
  
    diagonal.projection = function(x) {
      return arguments.length
          ? projection_(d3_svg_diagonalRadialProjection(projection = x))
          : projection;
    };
  
    return diagonal;
  };
  
  function d3_svg_diagonalRadialProjection(projection) {
    return function() {
      var d = projection.apply(this, arguments),
          r = d[0],
          a = d[1] + d3_svg_arcOffset;
      return [r * Math.cos(a), r * Math.sin(a)];
    };
  }
  