docs: fix `ngProjectAs` selector in example (#42523)

Fixes #42522

PR Close #42523

aio/content/examples/content-projection/src/app/app.component.html

@@ -34,7 +34,7 @@
 <app-zippy-ngprojectas>
   <p>Let's learn about content projection!</p>
   <!-- #docregion ngprojectas-->
-  <ng-container ngProjectAs="question">
+  <ng-container ngProjectAs="[question]">
     <p>Is content projection cool?</p>
   </ng-container>
   <!-- #enddocregion-->

aio/content/examples/content-projection/src/app/zippy-multislot/zippy-multislot.component.ts

@@ -4,7 +4,9 @@ import { Component } from '@angular/core';
   selector: 'app-zippy-multislot',
   template: `
   <h2>Multi-slot content projection</h2>
+  Default:
   <ng-content></ng-content>
+  Question:
   <ng-content select="[question]"></ng-content>
 `
 })

aio/content/examples/content-projection/src/app/zippy-ngprojectas/zippy-ngprojectas.component.ts

@@ -4,7 +4,9 @@ import { Component } from '@angular/core';
   selector: 'app-zippy-ngprojectas',
   template: `
   <h2>Content projection with ngProjectAs</h2>
+  Default:
   <ng-content></ng-content>
+  Question:
   <ng-content select="[question]"></ng-content>
 `
 })

aio/content/guide/content-projection.md

@@ -154,4 +154,4 @@ The `ng-container` element is a logical construct that you can use to group othe
 
 </div>
 
-In this example, the content we want to project resides inside another element. To project this content as intended, the template uses the `ngProjectAs` attribute. With `ngProjectAs`, the entire `ng-container` element is projected into a component using the `question` selector.
+In this example, the content we want to project resides inside another element. To project this content as intended, the template uses the `ngProjectAs` attribute. With `ngProjectAs`, the entire `ng-container` element is projected into a component using the `[question]` selector.