code: function (x, y, r) {
      return new BVG('circle', x.constructor.name === 'Object' ? x : {
        x: x,
        y: y,
        r: r
      }, function (tag, data) {
        tag.setAttribute('cx', data.x);
        tag.setAttribute('cy', data.y);
        tag.setAttribute('r', data.r);
      });
    }
docs: ### `bvg.circle(cx, cy, r)`
  Create a circle centred on `(cx, cy)` with radius `r`.
  
  ```Javascript
  var circle = bvg.ellipse(100, 100, 50);
  ```