<tr mat-header-row *matHeaderRowDef="columnsToDisplay"></tr>
 <tr mat-row *matRowDef="let element; columns: columnsToDisplay;"
     class="example-element-row"
     [class.example-expanded-row]="expandedElement === element"
     (click)="expandedElement = element">
 </tr>
 <tr mat-row *matRowDef="let row; columns: ['expandedDetail']" class="example-detail-row"></tr>
</table>