Further advanced validation rule example

Author: AndyButland

13/umbraco-forms/editor/creating-a-form/form-advanced.md

@@ -22,6 +22,8 @@ To add new rules, you need to provide the rule definition, an error message and
 
 Crafting the rule definition itself requires use of [JSON logic](https://jsonlogic.com/) along with placeholders for the field or fields that are being validated.
 
+### Examples
+
 One example use case would be ensuring that two fields match each other, perhaps when asking for a user's email address.  Given two fields on the form, one with the alias of `email` and the other `compareEmail`, the rule would be:
 
 ```json
@@ -60,6 +62,37 @@ A slightly more complex example could be with two dates, where, if provided, you
 }
 ```
 
+Rules can be nested too. In this final illustrative example, we have two fields. One with the alias `choose` is a drop-down list with two values: `A` and `B`. The second field with alias `test` we want to be completed only if the user selects `B`.  So we craft a rule that is valid only if A is selected OR B is selected AND `test` is completed.
+
+```json
+{
+  "or": [
+    {
+      "==": [
+        "{choose}",
+        "A"
+      ]
+    },
+    {
+      "and": [
+        {
+          "==": [
+            "{choose}",
+            "B"
+          ]
+        },
+        {
+          "!=": [
+            "{test}",
+            ""
+          ]
+        }
+      ]
+    }
+  ]
+}
+```
+
 Overall you should be able to create simple or more complex rules as needed, using comparisons between fields and with static values.
 
 When the form is rendered, these validation rules will be applied both client and server-side. In this way you can ensure the submission is only accepted if it meets the requirements.