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ElementInternals — form-associated custom elements
Check what you took from the post: why plain custom elements are invisible to <form>, what static formAssociated and attachInternals() actually unlock, and where the hidden-input hack quietly falls apart.
questions7
pass mark70%
resultsat the end
No account needed. Answer all 7 questions, then see your score with every answer explained and a reference to the spec or MDN — pass and you can claim a certificate.