message: docs: move hierarchical injectors to reference section
  PR Close
diff: "title": "Angular Dependency Injection",
  "tooltip": "Angular's dependency injection system creates and delivers dependent services to Angular-created classes."
  },
  - {
  - "url": "guide/hierarchical-dependency-injection",
  - "title": "Hierarchical Injectors",
  - "tooltip": "An injector tree parallels the component tree and supports nested dependencies."
  - },
  {
  "url": "guide/dependency-injection-providers",
  "title": "DI Providers",
  "tooltip": "How observables compare to promises and other message passing techniques."
  }
  ]
  + },
  + {
  + "url": "guide/hierarchical-dependency-injection",
  + "title": "Hierarchical Injectors",
  + "tooltip": "An injector tree parallels the component tree and supports nested dependencies."
  }
  ]
  },
  