chore: document oninput type for elements.d.ts (#12088)

packages/svelte/elements.d.ts

@@ -113,6 +113,7 @@ export interface DOMAttributes<T extends EventTarget> {
 	'on:beforeinput'?: EventHandler<InputEvent, T> | undefined | null;
 	onbeforeinput?: EventHandler<InputEvent, T> | undefined | null;
 	onbeforeinputcapture?: EventHandler<InputEvent, T> | undefined | null;
+	// oninput can be either an InputEvent or an Event, depending on the target element (input, textarea etc).
 	'on:input'?: FormEventHandler<T> | undefined | null;
 	oninput?: FormEventHandler<T> | undefined | null;
 	oninputcapture?: FormEventHandler<T> | undefined | null;