Indeed. This is the relevant part of the specification: https://html.spec.whatwg.org/multipage/custom-elements.html#valid-custom-element-name https://html.spec

Indeed. This is the relevant part of the specification: https://html.spec.whatwg.org/multipage/custom-elements.html#valid-custom-element-name https://html.spec.whatwg.org/multipage/custom-elements.html#...