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