Svelte 5: Cannot set <details> element to open initially using bind

[vak0160]

Describe the bug

I can't set <details> element to open initially on svelte 5, but it works correctly on svelte 4. Checkbox element works as usual.

Reproduction

svelte 5:
https://svelte-5-preview.vercel.app/#H4sIAAAAAAAACpWRwWrEIBCGX2WQHloo5G7dhULfotmDibN0qDGik6Uh5N3rGEsPhYWedOb3_-Yf3NSVPGal3zcV7IRKq9cY1bPiNUqRb-gZS53nJY3SMXlMFPnch549MswRA5zgIbNlfOS04NMLQNcBBWKy3q-QyzOeQbQf1_iB4ye6_xhN9zs5GIdsyWcYKDgtGWogk5dpsmk9vx1y8bSGqH_A4hNwgx1kCnEpatn_1Kuac5i_enVMarm7FoJuFSwcDZsc-_3dzZCqlxuouNrtrrFErKPKR0yzoyuhU1qk_bJ_A9kQF63DAQAA

svelte 4:
https://svelte.dev/repl/54b9e195e79745aca168d6d9a3d38805?version=4.2.3

Logs

No response

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (16) x64 AMD Ryzen 7 5700X 8-Core Processor
    Memory: 22.60 GB / 31.91 GB
  Binaries:
    Node: 20.3.1 - C:\Program Files\nodejs\node.EXE
    npm: 8.19.2 - C:\Program Files\nodejs\npm.CMD
    pnpm: 8.10.5 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Spartan (44.19041.3636.0), Chromium (119.0.2151.58)
    Internet Explorer: 11.0.19041.3636

Severity

annoyance

[brunnerh]

Looks like an issue with bind:, one way works as expected:

<details {open} ontoggle={e => open = e.target.open}>
	<summary>Details</summary>
	initially set to open
</details>

REPL

[CharlBest]

@navorite I think this is an issue with the <dialog> element as well. It also contains an open attribute.
Snippet from MDN Dialog Html element

<dialog open>
  <p>Greetings, one and all!</p>
  <form method="dialog">
    <button>OK</button>
  </form>
</dialog>

REPL

[brunnerh]

A simple implementation of a binding would not be possible because the events API is not symmetrical.
Dialog only supplies a close event and not one for opening.

I suppose a MutationObserver could be used as the open state is reflected as an attribute.

REPL

[CharlBest]

Thanks @brunnerh
That makes sense. Didn't think about that.