Generic HTML Sanitizer Bypass Investigation

I stumbled over a weird HTML behavior on Twitter and started to investigate it. Did I just stumble over a generic HTML Sanitizer bypass?

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The Tweet: https://twitter.com/MRCodedBrain/status/1662701541680136195
Google XSS: https://www.youtube.com/watch?v=lG7U3fuNw3A
HTML Spec: https://html.spec.whatwg.org/multipage/parsing.html#parse-error-invalid-first-character-of-tag-name

Chapters:
00:00 - Intro
01:09 - Sanitizing vs. Encoding
02:32 - Developing HTML Sanitizer Bypass
05:03 - Attacking DOMPurify
07:08 - Attacking Server-side Sanitizer
08:31 - HTML Parse Error Specification
10:08 - Potential Impact
11:55 …

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