The key is the ID of a form element X. The value is an array of the IDs of all form elements that must be equal to X.
The key is the ID of a form element X. The value is an array of the IDs of all form elements that are in the same required group as X.
The key is the ID of a form element X. The value is an array of the IDs of all form elements that are hidden or visible depending on the value of X.
The key is the ID of a form element X. The value is an array of the IDs of all form elements that are disabled or ensabled depending on the value of X.
The key is the ID of a form element X. The value is an array of the IDs of all form elements that are required or optional depending on the value of X.
The configuration that describes which elements reference other form elements. For example, an elment might be visible or hidden depending on the value of another element.