# ElementRef

Optional ref contract shared by DOM-backed component options.

## Signatures

```ts
export type ElementRef<Element extends globalThis.Element> = {
    readonly ref?: ElementRefCallback<Element> | RefSubject.HydrationRef<any, any>;
};
```

## Why

It supports both ordinary element callbacks and a `RefSubject` hydration
owner at the same host boundary.

## Ownership and lifetime

A mounted element may have only one hydration owner. Composed ordinary refs
share the rendering Scope and must not outlive the element.

## Property: ref

The callback or sole hydration owner for the mounted element.