# #id?

## `#id?`

An optional collection of unique allowed [identification](https://error.angular-package.dev/getting-started/basic-concepts#unique-identification) numbers of generic type variable [`Id`](https://error.angular-package.dev/generic-type-variables#commonerrors-less-than-id-greater-than) under which errors are stored.

{% code title="common-errors.class.ts" %}

```typescript
#id?: Set<Id>;
```

{% endcode %}

### Type

#### `Set<`[<mark style="color:green;">`Id`</mark>](https://error.angular-package.dev/generic-type-variables#commonerrors-less-than-id-greater-than)`>`