Allow resources from the same origin as the Jenkins instance (the 'self' keyword).

This is a good, safe default option for most directives, as it restricts resource loading and navigation to the same domain, protocol, and port as Jenkins itself. Note that this can be unsafe when not setting a resource root URL: Users can place, e.g., script files in job workspaces, which would be considered to be from the same origin.

Note: For most directives, 'self' is already set by default in Jenkins. You typically only need to add this explicitly after using a reset rule.