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Structural directives change the layout of the HTML document by adding and removing elements. They build on the core features available for attribute directives, described in Chapter 15, with additional support for micro-templates, which are small fragments of contents defined within the templates used by components. You can recognize when a structural directive is being used because its name will be prefixed with an asterisk, such as *ngIf and *ngFor. In this chapter, I explain how structural directives are defined and applied, how they work, and how they respond to changes in the data model. Table 16-1 puts structural directives in context.

Tag helpers are a new feature that has been introduced in ASP.NET Core MVC and are C# classes that transform HTML elements in a view. Common uses for tag helpers include generating URLs for forms using the application’s routing configuration, ensuring that elements of a specific type are styled consistently, and replacing custom shorthand elements with commonly used fragments of content. In this chapter, I describe how tag helpers work and how custom tag helpers are created and applied.