Describe the bug

Hello! I found out that Svelte does not use the set_custom_element_data helper when spreading a variabile to a custom element.
In particular, this doesn't work for camel case properties because the set_attributes method lowercases the property name. I'm not sure if this is the expected behavior. If so, I think it might be better to check that the attribute is among the element's setters before calling normalize_attribute here.

Reproduction

https://svelte.dev/playground/707b184533634e3fad230e91eecd3901?version=5.38.0

Logs

System Info

REPL

Severity

annoyance