doc(howTo.pages.actuator): add notes about whiteLabelErrorPage

spring-boot-project/spring-boot-docs/src/docs/antora/modules/how-to/pages/actuator.adoc

@@ -18,27 +18,28 @@ Spring Boot Actuator
 
 [[howto.actuator.customize-whitelabel-error-page]]
 == Customize the '`whitelabel`' Error Page
-* TODO:
-Spring Boot installs a '`whitelabel`' error page that you see in a browser client if you encounter a server error (machine clients consuming JSON and other media types should see a sensible response with the right error code).
-
-NOTE: Set `server.error.whitelabel.enabled=false` to switch the default error page off.
-Doing so restores the default of the servlet container that you are using.
-Note that Spring Boot still tries to resolve the error view, so you should probably add your own error page rather than disabling it completely.
-
-Overriding the error page with your own depends on the templating technology that you use.
-For example, if you use Thymeleaf, you can add an `error.html` template.
-If you use FreeMarker, you can add an `error.ftlh` template.
-In general, you need a `View` that resolves with a name of `error` or a `@Controller` that handles the `/error` path.
-Unless you replaced some of the default configuration, you should find a `BeanNameViewResolver` in your `ApplicationContext`, so a `@Bean` named `error` would be one way of doing that.
-See {code-spring-boot-autoconfigure-src}/web/servlet/error/ErrorMvcAutoConfiguration.java[`ErrorMvcAutoConfiguration`] for more options.
-
-See also the section on xref:reference:web/servlet.adoc#web.servlet.spring-mvc.error-handling[] for details of how to register handlers in the servlet container.
+* '`whitelabel`' error page
+    ** installed by Spring Boot
+    ** if you encounter a server error &
+        *** browser client -> '`whitelabel`' error page displayed
+        *** machine clients / consuming JSON and other media types -> sensible response / right error code
+    ** if you set `server.error.whitelabel.enabled=false`  -> 👁️switch off the default error page 👁️ ->
+        *** you must handle it / exists `BeanNameViewResolver` in your `ApplicationContext` (== `@Bean` named `error`)
+            **** Reason: 🧠 Spring Boot still tries to resolve the error view 🧠
+            **** overriding the error -- via -- templating technology
+                ***** Thymeleaf -- adding an -- `error.html` template
+                ***** FreeMarker -- adding an -- `error.ftlh` template
+            **** `View` / -- resolves with a name of -- `error` OR
+            **** `@Controller` / handles the `/error` path
+            **** Check
+                ***** {code-spring-boot-autoconfigure-src}/web/servlet/error/ErrorMvcAutoConfiguration.java[`ErrorMvcAutoConfiguration`] for more options
+                ***** xref:reference:web/servlet.adoc#web.servlet.spring-mvc.error-handling[] -- how to register handlers in the servlet container?
 
 
 
 [[howto.actuator.customizing-sanitization]]
 == Customizing Sanitization
-
+* TODO:
 To take control over the sanitization, define a `SanitizingFunction` bean.
 The `SanitizableData` with which the function is called provides access to the key and value as well as the `PropertySource` from which they came.
 This allows you to, for example, sanitize every value that comes from a particular property source.