https://developer.mozilla.org/en-US/docs/Web/API/ShadowRoot/innerHTML
ShadowRoot: innerHTML property - Web APIs | MDN
The innerHTML property of the ShadowRoot interface gets or sets the HTML markup to the DOM tree inside the ShadowRoot.
web apisinnerhtmlpropertymdn
https://shadowroot-streams.deno.dev/
ShadowRoot Streams
streams
https://bugzilla.mozilla.org/show_bug.cgi?id=1723521
1723521 - Implement and ship ElementInternals.shadowRoot
implementship