The third categorization of directives, structural directives, work on the components/elements to manipulate their layout.
The Angular documentation describes structural directives in a succinct manner:
"Instead of defining and controlling a view like a Component Directive, or modifying the appearance and behavior of an element like an Attribute Directive, the Structural Directive manipulates the layout by adding and removing entire element sub-trees."
Since we have already touched upon component directives (such as workout-runner and exercise-description) and attribute directives (such as ngClass and ngStyle), we can very well contrast their behaviors with structural directives.
The ngFor directive belongs to this class. We can easily identify such directives by the * prefix. Other than ngFor, Angular comes with some other structural directives such as ngIf and ngSwitch.