Lateral Fallback

A field falls back to the value of another field, or chain of fields

Configuration

1. If a template has a field that requires lateral fallback then that template must be based on the /sitecore/templates/System/Templates/Fallback template template not /sitecore/templates/System/Templates/Standard template
2. Go to the __standard values of the template or the item itself and make sure View -> Standard Fields is checked.
3. You should see a "Fallback" section that has a Name Value List field type.
4. The Key is the field that gets a fallback value. The Value is a '|' separated list of fields to inspect for a value.