Angular2 Directive - selector with multiple ids
<p>I'm implementing a custom directive in Angular 2, directive for form validation, and in many places I see that in the directive definition the selector property is associated with multiple ids - for example:</p>

<pre><code>@Directive({
    selector: '[my-custom-validator][ngModel]'
})
</code></pre>

<p>What does the multiple '[...]' (brackets) selection mean?</p>