Structural directives deal with modifying elements in the DOM by adding new elements, removing existing elements, and replacing existing elements with new elements. The following markup shows two structural directives: *ngFor and *ngIf:

<div *ngFor="#todo of todos"></div> 
<todo-item *ngIf="selectedTodo"></todo-item> 

*ngFor iterates through each item in the todos collection and adds a div tag for each item. And *ngIf renders <todo-item> only if selectedTodo is available.