Svelte Custom element API

I have doubts about how to create a Custom element API. I have followed the documentation, but I get the following warning:

The 'tag' option is used when generating a custom element. Did youforget the 'customElement: true' compile option? (Link.svelte: 1:16)

REPL

I have marked customElement: true in compiler options.

I'm lost, can anyone help me?