Root XML element name comes from component name

Clarifies that the name of the root XML element comes from
the component name, which was shown in an example but was unclear
due to the use of the obsolete OAS 2.0 terminology "model."

This does not change the restriction (in the `xml` field of the
Schema Object) that the `xml` field only applies to property
schemas (and not root schemas).

Author: handrews

src/oas.md

@@ -3253,22 +3253,25 @@ animals:
 
 ###### XML Attribute, Prefix and Namespace
 
-In this example, a full model definition is shown.
+In this example, a full [schema component](#components-schemas) definition is shown.
+Note that the name of the root XML element comes from the component name.
 
 ```yaml
-Person:
-  type: object
-  properties:
-    id:
-      type: integer
-      format: int32
-      xml:
-        attribute: true
-    name:
-      type: string
-      xml:
-        namespace: https://example.com/schema/sample
-        prefix: sample
+components:
+  schemas:
+    Person:
+      type: object
+      properties:
+        id:
+          type: integer
+          format: int32
+          xml:
+            attribute: true
+        name:
+          type: string
+          xml:
+            namespace: https://example.com/schema/sample
+            prefix: sample
 ```
 
 ```xml