alias: refPoints

Set the `points` attribute of the `<polygon>` or `<polyline>` subelement relatively to the dimensions and position of the element referenced by the selector in the `ref` attribute. The `refPoints` are scaled so that the subelement's dimensions match the reference element's dimensions, and translated so that the their origin matches the origin of the reference element.

The original points offset is not preserved. This means that if the top-left corner of the `refPoints` bounding box does not lie at `0,0`, the subelement is translated so that this gap disappears. The rendered subelement then fits perfectly into the reference element's bounding box.

    var Polygon = joint.dia.Element.define('examples.Polygon', {
        attrs: {
            polygon: {
                refPoints: '10,10 30,10 30,30', // points offset of 10,10 will be discarded
                fill: 'red',
                stroke: 'black'
            }
        }
    }, {
        markup: 'polygon'
    });

    var p = (new Polygon()).resize(40, 40).addTo(graph);
    // the rendered polygon's `points` attribute will be '0,0 40,0 40,40'
    // can be obtained by `p.findView(paper).vel.findOne('polygon').attr('d');`