Update readme.md

Expanded and clarified the Readme. Also included in the description the updated script.

Author: WillemZeiler

Specialized Areas/Regular Expressions/Check for special characters/readme.md

@@ -1 +1,26 @@
+# Special Characters Validation (onChange Client Script)
+
+This script validates user input in a specific field and prevents the use of disallowed special characters.  
+It is designed to run as an **onChange client script** .
+
+## Functionality
+
+- When the user changes the value of a field, the script checks if the new value contains any special characters.
+- If disallowed characters are found, the field is cleared and an error message is displayed to the user.
+- The validation uses a regular expression that includes common special characters such as `~`, `@`, `|`, `$`, `^`, `<`, `>`, `*`, `+`, `=`, `;`, `?`, `` ` ``, `'`, `(`, `)`, `[`, and `]`.
+
+## How to Use
+
+1. Add the script as an **onChange client script** on the field you want to validate.
+2. Replace the placeholder `'<your_field_name>'` in the script with the actual field name.
+3. Customize the regular expression if you want to allow or block different characters.
+
+## Example Behavior
+
+- Input: `Hello@World` → ❌ Invalid → Field is cleared, error message shown.
+- Input: `HelloWorld` → ✅ Valid → No action taken.
+
+## Notes
+
+- The script uses `g_form.clearValue()` to reset the field and `g_form.showErrorBox()` to display feedback.