Merge pull request #8488 from docker/master

Sync published with master

_includes/content/compose-extfields-sub.md

@@ -8,7 +8,7 @@ your Compose file and their name start with the `x-` character sequence.
 > (for the 2.x series), extension fields are also allowed at the root
 > of service, volume, network, config and secret definitions.
 
-```none
+```yaml
 version: '3.4'
 x-custom:
   items:
@@ -24,7 +24,7 @@ inserted in your resource definitions using [YAML anchors](http://www.yaml.org/s
 For example, if you want several of your services to use the same logging
 configuration:
 
-```none
+```yaml
 logging:
   options:
     max-size: '12m'
@@ -34,7 +34,7 @@ logging:
 
 You may write your Compose file as follows:
 
-```none
+```yaml
 version: '3.4'
 x-logging:
   &default-logging
@@ -55,7 +55,7 @@ services:
 It is also possible to partially override values in extension fields using
 the [YAML merge type](http://yaml.org/type/merge.html). For example:
 
-```none
+```yaml
 version: '3.4'
 x-volumes:
   &default-volume

_includes/content/compose-var-sub.md

@@ -3,8 +3,10 @@ variable values from the shell environment in which `docker-compose` is run. For
 example, suppose the shell contains `POSTGRES_VERSION=9.3` and you supply this
 configuration:
 
+```yaml
 db:
   image: "postgres:${POSTGRES_VERSION}"
+```
 
 When you run `docker-compose up` with this configuration, Compose looks for the
 `POSTGRES_VERSION` environment variable in the shell and substitutes its value
@@ -47,9 +49,11 @@ dollar sign. This also prevents Compose from interpolating a value, so a `$$`
 allows you to refer to environment variables that you don't want processed by
 Compose.
 
+```yaml
 web:
   build: .
   command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
+```
 
 If you forget and use a single dollar sign (`$`), Compose interprets the value
 as an environment variable and warns you:

compose/compose-file/compose-file-v2.md

@@ -197,6 +197,10 @@ or a list:
         - buildno=1
         - gitcommithash=cdc3b19
         
+> **Note**: In your Dockerfile, if you specify `ARG` before the `FROM` instruction, 
+> If you need an argument to be available in both places, also specify it under the `FROM` instruction.
+> See [Understand how ARGS and FROM interact](/engine/reference/builder/#understand-how-arg-and-from-interact) for usage details.
+
 You can omit the value when specifying a build argument, in which case its value
 at build time is the value in the environment where Compose is running.
 

develop/develop-images/build_enhancements.md

@@ -23,7 +23,7 @@ For more information on build options, see the reference guide on the [command l
 ## Limitations
 
 * BuildKit mode is incompatible with UCP and Swarm Classic
-* Only supported on Linux
+* Only supported for building Linux containers
 
 ## To enable buildkit builds
 

ee/dtr/user/manage-images/sign-images/trust-with-remote-ucp.md

@@ -226,6 +226,7 @@ Orchestrator as there is no SSO between cluster 2 and DTR. See the relevant
 
 ### Example Errors
 
+#### Image or trust data does not exist
 ```
 image or trust data does not exist for dtr.example.com/admin/trustdemo:1
 ```
@@ -233,6 +234,8 @@ image or trust data does not exist for dtr.example.com/admin/trustdemo:1
 This means something went wrong when initiating the repository or signing the
 image, as the tag contains no signing data. 
 
+#### Image did not meet required signing policy
+
 ```
 Error response from daemon: image did not meet required signing policy
 
@@ -243,6 +246,14 @@ This means that the image was signed correctly, however the user who signed the
 image does not meet the signing policy in cluster 2. This could be because you
 signed the image with the wrong user keys.
 
+#### DTR URL must be a registered trusted registry
+
+```
+Error response from daemon: dtr.example.com must be a registered trusted registry.
+```
+
+This means you have not registered DTR to work with a remote UCP instance yet, as outlined in [Registering DTR with a Remote Universal Control Plane](#registering-dtr-with-a-remote-universal-control-plane).
+
 ## Where to go next
 
 - [Learn more about Notary](/notary/advanced_usage.md)