Read and write field values.
Form field. Can either be a group of named fields, or a final field.
Build a field from its value.
Build a string field, for text inputs, selects, etc.
Build a boolean field, for checkboxes.
Gather named fields as a group field.
Gather fields as a list field.
Get field value as string.
Get field value as boolean.
A field is a tree node.