Mastodawn

I think `shadowrootcustomelementregistry` just took the lead in the longest HTML attribute race:
https://developer.mozilla.org/en-US/docs/Web/API/HTMLTemplateElement/shadowRootCustomElementRegistry

…though still comfortably beaten by your average German compound noun 😄

HTMLTemplateElement: shadowRootCustomElementRegistry property - Web APIs | MDN

The shadowRootCustomElementRegistry property of the HTMLTemplateElement interface reflects the value of the shadowrootcustomelementregistry attribute of the associated <template> element.

MDN Web Docs