anchor.diff:  :marked
     Each overide method takes a `MetadataOverride<T>` where `T` is the kind of metadata
     appropriate to the method, the parameter of an `@NgModule`, `@Component`, `@Directive`, or `@Pipe`.
  +
  +
   
   code-example(format="." language="javascript").
     type MetadataOverride<T> = {
  
positive.code:   A metadata override object can either add-and-remove elements in metadata properties or completely reset those properties.
    This example resets the component's `providers` metadata.
  
    元数据替换对象可以添加和删除元数据属性的项目，也可以彻底重设这些属性。
    这个例子重新设置了组件的`providers`元数据。
  
    The type parameter, `T`,  is the kind of metadata you'd pass to the `@Component` decorator:
  
negative.code: 
    1. [Override component providers](#component-override)
  
    1. [重载组件提供商](#component-override)
    <br>
  
    1. [Test a _RouterOutlet_ component](#router-outlet-component)
  