docs: update swagger-other-features docs

Author: Kimsunmin

content/openapi/other-features.md

@@ -93,3 +93,84 @@ Navigate to `http://localhost:3000/api/cats` to see the Swagger UI for cats:
 In turn, `http://localhost:3000/api/dogs` will expose the Swagger UI for dogs:
 
 <figure><img src="/assets/swagger-dogs.png" /></figure>
+
+#### Multiple specifications from dropdown in the explorer bar
+
+To support multiple specifications from dropdown in the explorer bar, you need to use `explorer: true` and `swaggerOptions.urls` in `SwaggerCustomOption`.
+
+> info **Tip** `swaggerOptions.urls` must use the url of the swagger document in json format! To use json for specifications, use `jsonDocumentUrl` in `SwaggerCustomOption`.
+more setup options [here](/openapi/introduction#setup-options)
+
+You can setup multiple specifications from dropdown in the explorer barsupport as shown below
+```typescript
+import { NestFactory } from '@nestjs/core';
+import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';
+import { AppModule } from './app.module';
+import { CatsModule } from './cats/cats.module';
+import { DogsModule } from './dogs/dogs.module';
+
+async function bootstrap() {
+  const app = await NestFactory.create(AppModule);
+
+  const options = new DocumentBuilder()
+    .setTitle('Multiple specifications example')
+    .setDescription('The multiple specifications description')
+    .setVersion('1.0')
+    .build();
+
+  const document = SwaggerModule.createDocument(app, options);
+  SwaggerModule.setup('api', app, document, {
+    // This option is set to 'true' for the dropdown to be visible.
+    explorer: true,
+
+    swaggerOptions: {
+      urls: [
+        {
+          name: '1. API',
+          url: 'api/swagger.json',
+        },
+        {
+          name: '2. Cats API',
+          url: 'api/cats/swagger.json',
+        },
+        {
+          name: '3. Dogs API',
+          url: 'api/dogs/swagger.json',
+        },
+      ],
+    },
+    jsonDocumentUrl: '/api/swagger.json',
+  });
+
+  const catOptions = new DocumentBuilder()
+    .setTitle('Cats example')
+    .setDescription('The cats API description')
+    .setVersion('1.0')
+    .addTag('cats')
+    .build();
+
+  const catDocument = SwaggerModule.createDocument(app, options, {
+    include: [CatsModule],
+  });
+  SwaggerModule.setup('api/cats', app, catDocument, {
+    jsonDocumentUrl: '/api/cats/swagger.json',
+  });
+
+  const dogOptions = new DocumentBuilder()
+    .setTitle('Dogs example')
+    .setDescription('The dogs API description')
+    .setVersion('1.0')
+    .addTag('dogs')
+    .build();
+
+  const dogDocument = SwaggerModule.createDocument(app, dogOptions, {
+    include: [DogsModule],
+  });
+  SwaggerModule.setup('api/dogs', app, dogDocument, {
+    jsonDocumentUrl: '/api/dogs/swagger.json',
+  });
+
+  await app.listen(3000);
+}
+bootstrap();
+```