Svelte docs: document defaultValue

[theetrain]

Special element attributes defaultValue and defaultChecked (maybe there are others?) don't appear to be documented. I could see this being its own page, or an addendum to some existing pages.

I see these as special since although they've available through the DOM API, Svelte allows them to be set as attributes that work well with bind:value or assigning value to either a string or nullish value.

Applicable pages:

• Basic markup: https://svelte.dev/docs/svelte/basic-markup
• New page, "Enhanced markup"?
• Progressive enhancement: https://svelte.dev/docs/kit/form-actions#Progressive-enhancement
• Tutorial, Bindings: https://svelte.dev/tutorial/svelte/text-inputs

[hyunbinseo]

I agree that a independent documentation is needed.

I just learned that these Svelte markups:

<input type="checkbox" defaultChecked />
<input type="checkbox" defaultChecked={true} />

are both server rendered as <input type="checkbox"/>, which is not what I expected.

Currently, these attributes are only mentioned in the bind: section and are not searchable.

• Cannot search defaultValue or defaultChecked #1364