   set. The document parser uses this algorithm.
2. In [invoke custom element reactions], step 2.1.

There are different code paths when:
1. Author script throws an exception that is rethrown.
2. The user agent throws an exception.

This test contains 4 tests for the combination of the above 2x2.

[create an element]: https://dom.spec.whatwg.org/#concept-create-element
[create an element for a token]: https://html.spec.whatwg.org/multipage/syntax.html#create-an-element-for-the-token
[invoke custom element r