The `ui-mask` in `Angular UI Utils' project ([link](http://angular-ui.github.io/ui-utils/)) is a bit too limited. 

For example, the first digit of a US phone number should be 2-9. In `ngPattern`, it should be 

```
ng-pattern="/^\([2-9]\d{2}\)\d{3}-\d{4}(x\d{1,4})?$/"

```

So how can I write an input mask to prevent users from entering 0 or 1 in the first digit? Is there some better input mask we should use for Angular?