Add MAML reference

Author: antonmedv

docs/maml.md

@@ -156,6 +156,40 @@ options are available (`remote_user`, `deploy_path`, `port`, `identity_file`,
 }
 ```
 
+### Labels
+
+Labels are key-value tags used by [selectors](selector.md). Define them as a nested object under `labels`:
+
+```maml
+{
+  hosts: {
+    "web.example.com": {
+      remote_user: "deployer"
+      labels: {
+        type: "web"
+        env: "prod"
+      }
+    }
+    "db.example.com": {
+      remote_user: "deployer"
+      labels: {
+        type: "db"
+        env: "prod"
+      }
+    }
+  }
+}
+```
+
+Run a task on every `prod` host:
+
+```bash
+$ dep deploy env=prod
+```
+
+`labels.<key>` and a top-level config key with the same name (e.g. `env`) are independent — the selector only
+looks at `labels`.
+
 ### Localhost
 
 Set `local: true` to register the entry as a localhost via `localhost()`:

docs/selector.md

@@ -143,18 +143,24 @@ task('info', function () {
 })->select('type=web|db,env=prod');
 ```
 
-## Labels in YAML
-
-YAML recipes support labels too:
-
-```yaml
-hosts:
-  web.example.com:
-    remote_user: deployer
-    env:
-      environment: production
-    labels:
-      env: prod
+## Labels in MAML
+
+[MAML](maml.md) recipes support labels too:
+
+```maml
+{
+  hosts: {
+    "web.example.com": {
+      remote_user: "deployer"
+      env: {
+        environment: "production"
+      }
+      labels: {
+        env: "prod"
+      }
+    }
+  }
+}
 ```
 
 Don't confuse `env` (a config key) with `labels.env` (a label). They are independent: