Structural Directives
https://angular.io/guide/structural-directives#template-input-variable
There are two other kinds of Angular directives, described extensively elsewhere: (1) components and (2) attribute directives.
A component manages a region of HTML in the manner of a native HTML element. Technically it‘s a directive with a template.
An attribute directive changes the appearance or behavior of an element, component, or another directive. For example, the built-in NgStyle directive changes several element styles at the same time.
You can apply many attribute directives to one host element. You can only apply one structural directive to a host element.
原文：https://www.cnblogs.com/oxspirt/p/10107963.html