code: function getSVGElement(id) {
    var el = document.getElementById(id);
    return el ? assertInstanceof(el, Element) : null;
  }
docs: TODO(devlin): This should return SVGElement, but closure compiler is missing those externs. 
  Alias for document.getElementById. Found elements must be SVGElements.
  @param {string} id The ID of the element to find.
  @return {Element} The found element or null if not found.