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fix: allow attributes on the title element #15983

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@jschaf jschaf commented May 22, 2025

The spec states the title element supports global attributes. https://html.spec.whatwg.org/#the-title-element

Reverts the title attribute validation introduced in #1721.

Fixes #5198.

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Tests and linting

The test plan is to re-use packages/svelte/tests/validator/samples/title-no-attributes. By removing errors.json, we test that svelte compiles the title element with attributes.

  • Run the tests with pnpm test and lint the project with pnpm lint

The tests pass, but pnpm lint failed with:

> [email protected] lint /opt/p/svelte
> eslint && prettier --check .


Oops! Something went wrong! :(

ESLint: 9.9.1

Error: Cannot find module '/opt/p/svelte/node_modules/.pnpm/[email protected]_svelte@packages+svelte/node_modules/svelte/compiler/index.js'
    at createEsmNotFoundErr (node:internal/modules/cjs/loader:1441:15)
    at finalizeEsmResolution (node:internal/modules/cjs/loader:1430:15)

@jschaf
fix: allow attributes on the title element
5b73606 
The spec states the title element supports global attributes.
https://html.spec.whatwg.org/#the-title-element

Reverts the title attribute validation introduced in sveltejs#1721.

Fixes sveltejs#5198.
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🦋 Changeset detected

Latest commit: 8740110

The changes in this PR will be included in the next version bump.

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Preview: https://svelte-dev-git-preview-svelte-15983-svelte.vercel.app/

@jschaf jschaf mentioned this pull request May 22, 2025
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@Rich-Harris
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Thank you. The aria-live thing seems like a good reason to have this but it's not quite as straightforward as this PR — you've removed the validation, but the <title> still won't have any attributes.

When you create a <title> in a component, Svelte doesn't actually create a <title> element and append it to the head, it instead sets document.title, because you're only supposed to have one. We could probably change that (each new <title> inside a <svelte:head> would be prepended to the <head> instead, and removed when the component was unmounted — browsers will do the right thing in that case) but we'd need to change the implementation in addition to removing the validation.

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jschaf commented May 22, 2025

Thank you. The aria-live thing seems like a good reason to have this but it's not quite as straightforward as this PR — you've removed the validation, but the <title> still won't have any attributes.

Ah, I see. I'll take a crack at rendering the attributes. Should I limit attributes to a subset?

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I don't think there's any reason to limit it, it's extra work to prevent something that someone might find useful in ways we don't anticipate.

I think the most interesting challenge here will be hydration, since in the (admittedly rare!) case of duplicate elements they need to be rendered in reverse order, so that 'later' <title> elements (e.g. in a +page.svelte) take precedence over 'earlier' ones (e.g. a fallback in a +layout.svelte). Quite why browsers work that way is a mystery, of course.

@jschaf
WIP: attempt to add render title attributes
8740110 
SSR is pretty straight-forward. The client side is more difficult since
the TitleElement doesn't have a node_id.
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jschaf commented May 22, 2025

I added SSR title tag attributes by cribbing code from RegularElement in the latest commit. Client-side rendering is trickier, and I could use some pointers.

The TitleElement doesn't have a reference to the HTML element because we didn't need one before. To call build_set_attributes, I need a node_id, from context.state.node.

The code for adding attributes is inlined in the client RegularElement. I extracted the smallest chunk of code into TitleElement to make it work.

  • How should I go about getting the node_id for a TitleElement?

  • Should I use RegularElement to render TitleElement?

  • I'm still using the assignment to document.title to set the title value. Should I keep that approach or append the title element to the head element
    The challenge with appending is that spec states multiple title tags are not allowed: The title tag may be used in "head element containing no other title elements."

@jschaf jschaf marked this pull request as draft May 22, 2025 23:14
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Allow attributes on the <title> element
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@jschaf @Rich-Harris