Improve "Extend your Compose file" (#19129)

* extends.md: Add trailing newline

* extends.md: Remove trailing whitespace

* extends.md: Correct reference to previously-named file

* extends.md: Correct YAML syntax

* extends.md: Use conventional YAML indentation

* extends.md: Wrap to 80 characters

* Update content/compose/multiple-compose-files/extends.md

---------

Co-authored-by: Allie Sadler <102604716+aevesdocker@users.noreply.github.com>

content/compose/multiple-compose-files/extends.md

@@ -7,28 +7,29 @@ aliases:
 - /compose/extends/
 ---
 
-Docker Compose's [`extends` attribute](../compose-file/05-services.md#extends) lets you share common configurations
-among different files, or even different projects entirely. 
+Docker Compose's [`extends` attribute](../compose-file/05-services.md#extends)
+lets you share common configurations among different files, or even different
+projects entirely.
 
-Extending services
-is useful if you have several services that reuse a common set of configuration
-options. With `extends` you can define a common set of service options in one
-place and refer to it from anywhere. You can refer to another Compose file and select a service you want to also use in your own application, with the ability to override some attributes for your own needs.
+Extending services is useful if you have several services that reuse a common
+set of configuration options. With `extends` you can define a common set of
+service options in one place and refer to it from anywhere. You can refer to
+another Compose file and select a service you want to also use in your own
+application, with the ability to override some attributes for your own needs.
 
 > **Important**
 >
-> When you use multiple Compose files, you must make sure all paths in the
-files are relative to the base Compose file. This is required because extend files need not be valid
-Compose files. Extend files can contain small fragments of configuration.
-Tracking which fragment of a service is relative to which path is difficult and
-confusing, so to keep paths easier to understand, all paths must be defined
-relative to the base file.
-{ .important }
+> When you use multiple Compose files, you must make sure all paths in the files
+are relative to the base Compose file. This is required because extend files
+need not be valid Compose files. Extend files can contain small fragments of
+configuration. Tracking which fragment of a service is relative to which path is
+difficult and confusing, so to keep paths easier to understand, all paths must
+be defined relative to the base file. { .important }
 
 ## How it works
 
-When defining any service in your `compose.yaml` file, you can declare that you are
-extending another service:
+When defining any service in your `compose.yaml` file, you can declare that you
+are extending another service:
 
 ```yaml
 services:
@@ -96,8 +97,8 @@ services:
 ### Example one
 
 Extending an individual service is useful when you have multiple services that
-have a common configuration. The example below is a Compose app with
-two services, a web application and a queue worker. Both services use the same
+have a common configuration. The example below is a Compose app with two
+services, a web application and a queue worker. Both services use the same
 codebase and share many configuration options.
 
 The `common.yaml` file defines the common configuration:
@@ -112,8 +113,8 @@ services:
     cpu_shares: 5
 ```
 
-The `docker-compose.yaml` defines the concrete services which use the
-common configuration:
+The `docker-compose.yaml` defines the concrete services which use the common
+configuration:
 
 ```yaml
 services:
@@ -139,9 +140,9 @@ services:
 
 ### Example two
 
-Another common use case for `extends` is running one off or administrative tasks against one
-or more services in a Compose app. This example demonstrates running a
-database backup.
+Another common use case for `extends` is running one off or administrative tasks
+against one or more services in a Compose app. This example demonstrates running
+a database backup.
 
 The `docker-compose.yml` defines the base configuration.
 
@@ -150,14 +151,14 @@ services:
   web:
     image: example/my_web_app:latest
     depends_on:
-       db
+      - db
 
   db:
     image: postgres:latest
 ```
 
-`docker-compose.admin.yml` adds a new service to run the database
-export or backup.
+`docker-compose.admin.yml` adds a new service to run the database export or
+backup.
 
 ```yaml
 services:
@@ -175,19 +176,21 @@ $ docker compose -f docker-compose.yml -f docker-compose.admin.yml \
   run dbadmin db-backup
 ```
 
-Compose extends files in
-the order they're specified on the command line.
+Compose extends files in the order they're specified on the command line.
 
 ## Exceptions and limitations
 
-`volumes_from` and `depends_on` are never shared between
-services using `extends`. These exceptions exist to avoid implicit
-dependencies; you always define `volumes_from` locally. This ensures
-dependencies between services are clearly visible when reading the current file.
-Defining these locally also ensures that changes to the referenced file don't
-break anything.
+`volumes_from` and `depends_on` are never shared between services using
+`extends`. These exceptions exist to avoid implicit dependencies; you always
+define `volumes_from` locally. This ensures dependencies between services are
+clearly visible when reading the current file. Defining these locally also
+ensures that changes to the referenced file don't break anything.
 
-`extends` is useful if you only need a single service to be shared and you are familiar with the file you're extending to, so you can to tweak the configuration. But this isn’t an acceptable solution when you want to re-use someone else's unfamiliar configurations and you don’t know about its own dependencies.
+`extends` is useful if you only need a single service to be shared and you are
+familiar with the file you're extending to, so you can to tweak the
+configuration. But this isn’t an acceptable solution when you want to re-use
+someone else's unfamiliar configurations and you don’t know about its own
+dependencies.
 
 ## Reference information