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let define: ( WebAPI.DOMAPI.customElementRegistry, ~name: string, ~constructor: WebAPI.DOMAPI.customElementConstructor, ~options: WebAPI.DOMAPI.elementDefinitionOptions=?,) => unit
let getName: ( WebAPI.DOMAPI.customElementRegistry, WebAPI.DOMAPI.customElementConstructor,) => string
let upgrade: ( WebAPI.DOMAPI.customElementRegistry, WebAPI.DOMAPI.node,) => unit
let whenDefined: ( WebAPI.DOMAPI.customElementRegistry, string,) => Promise.t<WebAPI.DOMAPI.customElementConstructor>