function getIsExtends(element) {
  let localName = element['localName'];
  let is = '', typeExtension = '';
  /*
  NOTE: technically, this can be wrong for certain svg elements
  with `-` in the name like `<font-face>`
  */
  if (localName) {
    if (localName.indexOf('-') > -1) {
      is = localName;
    } else {
      typeExtension = localName;
      is = (element.getAttribute && element.getAttribute('is')) || '';
    }
  } else {
    is = /** @type {?} */(element).is;
    typeExtension = /** @type {?} */(element).extends;
  }
  return {is, typeExtension};
}
@param {Element | {is: string, extends: string}} element
@return {{is: string, typeExtension: string}}