Issue Summary:
When embedding an iframe within the TinyMCE editor in Moodle, a sandbox parameter is automatically added. However, attempts to modify or remove this parameter are unsuccessful. If the sandbox attribute loads without any value (e.g., sandbox=""), an error occurs in the browser:

"Blocked script execution in '{URL}' because the document's frame is sandboxed and the 'allow-scripts' permission is not set."

This restriction prevents the iframe from loading properly and limits necessary functionality.

Steps to Reproduce:

1. Embed an iframe in the TinyMCE editor.
2. Attempt to save or modify the sandbox attribute.
3. Observe that the iframe fails to load correctly due to missing permissions.