Structural directives are the tools you use to shape the reality of your user interface, conditionally building or repeating parts of the page based on your state.
1The Removal Mechanism
It is a common misconception that *ngIf simply hides elements. In reality, it physically removes the element and its children from the DOM tree. This is a powerful performance optimization: if a large part of your page isn't needed, Angular doesn't waste resources keeping it in memory or checking it for changes. When the condition becomes true, Angular recreates the elements from scratch based on the template.
2The <ng-container> Trick
Angular has a strict rule: only one structural directive per element. This can be frustrating when you want to loop through a list AND check a condition on each item. The solution is <ng-container>. This is a logical grouping element that doesn't appear in the final HTML. By wrapping your code in an <ng-container>, you can apply one directive to the container and another to the element inside, keeping your DOM clean and valid.
