code: function createContainer(options) {
  
    options = assign({}, { width: '100%', height: '100%' }, options);
  
    var container = options.container || document.body;
  
    // create a <div> around the svg element with the respective size
    // this way we can always get the correct container size
    // (this is impossible for <svg> elements at the moment)
    var parent = document.createElement('div');
    parent.setAttribute('class', 'djs-container');
  
    assign(parent.style, {
      position: 'relative',
      overflow: 'hidden',
      width: ensurePx(options.width),
      height: ensurePx(options.height)
    });
  
    container.appendChild(parent);
  
    return parent;
  }
docs: Creates a HTML container element for a SVG element with
  the given configuration
  
  @param  {Object} options
  @return {HTMLElement} the container element