Added info on custom expression to compare values in a variable (#535)

Author: mahajantejas

docs/4. Product Features/03. Flows/2. Flow Actions/Split By/01. Custom Expression.md

@@ -4,7 +4,7 @@
     <tr>
       <td><b>4 minutes read</b></td>
       <td style={{ paddingLeft: 40 }}><b> Level: Intermediate</b></td>
-      <td style={{ paddingLeft: 40 }}><b>Last Updated: October 2025</b></td>
+      <td style={{ paddingLeft: 40 }}><b>Last Updated: December 2025</b></td>
     </tr>
   </table>
 </h3>
@@ -139,6 +139,17 @@ In the given example, the regex used is:
 
 <img width="582" height="400" alt="Screenshot 2025-10-08 at 4 59 57 PM" src="https://github.com/user-attachments/assets/6f345f13-af10-43fa-9a3d-759794c60523" />
 
+### 10. Comparing the values contained in variables.
+
+Example `<%= case "@results.assigned_arm_id" do "@results.control_arm_id" -> "Control"; "@results.treatment_arm_id" -> "Treatment"; end %>`
+
+This syntax enables to split based of if value in `@results.assigned_arm_id` matches either the value of present in `@results.control_arm_id` or `@results.treatment_arm_id`. 
+
+The expression creates two categories "Control" and "Treatment", like shown in the screenshot
+
+<img width="1360" height="1100" alt="image" src="https://github.com/user-attachments/assets/5b87521c-2acb-4892-8229-177d156009f4" />
+Similar syntax can be used to check for multiple variables. 
+
 ---
 
 ## Advanced Syntax Examples