Page transitions don't work if <a> tag has target attribute set (even to '_self')

[emmalexandria]

Describe the bug

Page transitions (achieved through a simple setup in +layout.svelte:

{#key data.pathname}
  <main in:fade={{ duration: 100, delay: 200 }} out:fade={{ duration: 100 }}>
    {@render children()}
  </main>
{/key}

will trigger when an <a> tag has no target set, but will not trigger when target is set to anything except undefined (including the default value of _self)

Reproduction

https://github.com/emmalexandria/transitions-repro

Logs

No response

System Info

System:
    OS: macOS 14.5
    CPU: (8) arm64 Apple M2
    Memory: 64.84 MB / 8.00 GB
    Shell: 3.7.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 23.2.0 - ~/.local/share/nvm/v23.2.0/bin/node
    npm: 10.9.0 - ~/.local/share/nvm/v23.2.0/bin/npm
    pnpm: 9.14.2 - ~/Library/pnpm/pnpm
  Browsers:
    Chrome: 131.0.6778.140
    Safari: 17.5
  npmPackages:
    @sveltejs/adapter-auto: ^3.0.0 => 3.3.1 
    @sveltejs/adapter-static: ^3.0.6 => 3.0.6 
    @sveltejs/kit: ^2.9.0 => 2.11.1 
    @sveltejs/vite-plugin-svelte: ^5.0.0 => 5.0.2 
    svelte: ^5.0.0 => 5.13.0 
    vite: ^6.0.0 => 6.0.3

Severity

annoyance

Additional Information

In custom link components, this little nit can be worked around by passing undefined to target instead of a default value of _self.

[dummdidumm]

Quoting Conduitry in #13165 (comment) :

Using target=_self as a way to indicate to an SPA framework that a given link should be treated normally rather than being intercepted predates SvelteKit. There are a number of frameworks that work this way. It may not have ever been documented in SK's docs - and there may be other official SK-specific ways of doing this - but I don't think we can just remove it. At the very least, removing this should be a breaking change.

So I'm not sure if we should be changing this

[fvarano]

If not changed, this should at least be documented.
I spent the last 4hrs figuring out why CSR was not working on one of our apps.

I understand the rationale behind the choice to keep this behavior, but:
_self is marked as the default option on MDN. So for developers, setting _self is just a way to give a good default in cases where that option comes from elsewhere, e.g. a headless CMS, not knowing that they're effectively disabling SvelteKit's navigation. Maybe a specific Link Option would be more appropriate to disable CSR for specific links.

[Conduitry]

There already is a specific SK link option that does this. I don't know which would be more appropriate. But I suspect there will still be people coming from other routing frameworks that will expect _self to work.