Using different types of Component Selector in Angular

Element Selector

selector: 'app-server1'

Attribute Selector

selector: '[app-server2]' // attribute selector

Class Selector

selector: '.app-server3' // class selector

Usage

<app-server1></app-server1> <!--element selector-->
<div app-server2></div> <!--attribute selector-->
<div class="app-server3"></div> <!--class selector-->

References
https://github.com/mhdr/AngularSamples/tree/master/003/my-app