function assertElement(assertFn, shouldBeElement, opt_message) {
  return /** @type {!Ele	ment} */ (
	  assertType_(
	    assertFn,
		  shouldBeElement,
		  isElement(shouldBeElement),
		  'Element expected',
		  opt_message
	  )
	);
}

const slot = /** @type {!HTMLSlotElement} */ (e.target);

assertElement(
  /** @type {Element} */ (el),
);
