# Invalid Shadow DOM selector

The selector of a component using `ViewEncapsulation.ShadowDom` doesn't match the custom element tag name requirements.

In order for a tag name to be considered a valid custom element name, it has to:

- Be in lower case.
- Contain a hyphen.
- Start with a letter \(a-z\).

## Debugging the error

Rename your component's selector so that it matches the requirements.

**Before:**

```ts
@Component({
  selector: 'comp',
  encapsulation: ViewEncapsulation.ShadowDom
…
})

```

**After:**

```ts
@Component({
  selector: 'app-comp',
  encapsulation: ViewEncapsulation.ShadowDom
…
})
```
