Update regular_expressions.md (#1115)

Identify the schema for the last example.
Identify the compliant and noncompliant data.
Make indentation consistent with the example above it.

Author: Vaent

pages/understanding-json-schema/reference/regular_expressions.md

@@ -85,14 +85,17 @@ The following example checks that the string starts with `{{` and ends with `}}`
 and that it also allows multiline strings.
 
 ```json
-   {
-      "type": "string",
-      "pattern": "^\\{\\{(.|[\\r\\n])*\\}\\}$",
-   }
+// props { "isSchema": true }
+{
+  "type": "string",
+  "pattern": "^\\{\\{(.|[\\r\\n])*\\}\\}$",
+}
 ```
 ```json
-   "{{ foo\nbar }}"
+// props { "indent": true, "valid": true }
+"{{ foo\nbar }}"
 ```
 ```json
-   "{ foo }"
+// props { "indent": true, "valid": false }
+"{ foo }"
 ```