What is Svelte doing internally to allow-for/require elective/explicit "DOM Event Forwarding"?

[metaleap]

After all, in a vanilla DOM, usually most events auto-propagate and bubble, unless scripter's explicit preventDefault/stopPropagation (the latter is enough, IIRC).

So if you were to re-create the Svelte example in non-Svelte, manually-scripted vanilla "Web Components"/"Custom Elements", not only would you not have to "event-forward" (whether via auto-generated or manually-written dispatchEvent code) — but also, if you did so, event consumers would just receive both the dispatched and the bubbled/auto-propagated click event (ie. 2x for a single click) — unless script code is written in-component to stopPropagation.

So my question is, what is Svelte doing to suppress that standard eventing behavior of the DOM — does it generate (or import+call) stopPropagation handlers for all or most documented event types, per component? I kinda like knowing what's happening "under the hood", but even the unminified Svelte-generated JS I usually just cannot really decipher/grok tbh.