Updated the $id and included a Draft-specific info box section

Author: Dule-martins

pages/understanding-json-schema/structuring.md

@@ -515,7 +515,7 @@ example bundled into a Compound Schema Document.
 
   "$defs": {
     "address": {
-      "$id": "/schemas/address",
+      "$id": "https://example.com/schemas/customer",
       "$schema": "http://json-schema.org/draft-07/schema#",
 
       "type": "object",
@@ -565,3 +565,10 @@ In Draft 4-7, a subschema `$id` is just a base URI change and not
    only allowed at the root of a Schema Resource, all schemas bundled
    using subschema `$id` must use the same dialect.
 </Infobox>
+
+<Infobox label="Draft-specific info">
+In Draft 2020-12,`$id` support for changing dialects in an embedded schema 
+   (using $schema with a different value than the parent schema) was added.
+   In 2020-09, Only URI-references without fragments are allowed;
+   all other fragments in $id had undefined behavior previously.   
+</Infobox>