Document spring.profiles.default in the reference guide

Closes gh-26592

Author: snicoll

spring-boot-project/spring-boot-docs/src/docs/asciidoc/howto.adoc

@@ -359,6 +359,22 @@ See "`<<spring-boot-features.adoc#boot-features-profiles>>`" in the "`Spring Boo
 
 
 
+[[howto-set-default-spring-profile-name]]
+=== Set the Default Profile Name
+The default profile is a profile that is enabled if no profile is active.
+By default, the name of the default profile is `default`, but it could be changed using a System property (configprop:spring.profiles.default[]) or an OS environment variable (configprop:spring.profiles.default[format=envvar]).
+
+In Spring Boot, you can also set the default profile name in `application.properties`, as shown in the following example:
+
+[source,properties,indent=0,subs="verbatim,quotes,attributes",configprops]
+----
+	spring.profiles.default=dev
+----
+
+See "`<<spring-boot-features.adoc#boot-features-profiles>>`" in the "`Spring Boot features`" section for more information.
+
+
+
 [[howto-change-configuration-depending-on-the-environment]]
 === Change Configuration Depending on the Environment
 Spring Boot supports multi-document YAML and Properties files (see <<spring-boot-features#boot-features-external-config-files-multi-document>> for details) which can be activated conditionally based on the active profiles.

spring-boot-project/spring-boot-docs/src/docs/asciidoc/spring-boot-features.adoc

@@ -1906,6 +1906,14 @@ For example, you could include it in your `application.properties`, as shown in
 
 You could also specify it on the command line by using the following switch: `--spring.profiles.active=dev,hsqldb`.
 
+If no profile is active, a default profile is enabled.
+The name of the default profile is `default` and it can be tuned using the configprop:spring.profiles.default[] `Environment` property, as shown in the following example:
+
+[source,properties,indent=0,configprops]
+----
+	spring.profiles.default=none
+----
+
 
 
 [[boot-features-adding-active-profiles]]