joint.dia.Paper is the view for the joint.dia.Graph model. It inherits from Backbone View. Accepts an options object in its constructor with numerous settings.

When a paper is associated with a graph, the paper makes sure that all the cells added to the graph are automatically rendered.

var graph = new joint.dia.Graph
var paper = new joint.dia.Paper({
    el: $('#paper'),
    width: 600,
    height: 400,
    gridSize: 10,
    model: graph
});

var rect = new joint.shapes.basic.Rect({
    position: { x: 50, y: 70 },
    size: { width: 100, height: 40 }
});

graph.addCell(rect);

Paper automatically handles this change and renders the rectangle to the SVG document that it internally holds.