Internal fields were not conceived as configurable since they were not instantiable. Consequently, the fields index does not provide any means of opening configuration form for internal fields.

However, an internal field could have configuration either by storing the data in the dataform table or some future dataform config table. The fields index therefore needs to allow configuring internal fields where applicable. Applicability can be determine in a similar way to other fields, that is, the presence of a field configuration form.

https://github.com/itamart/moodle-mod_dataform/commit/b0ef65732b7975ce7e9f68a7dfd0756fad2c111f
https://github.com/itamart/moodle-mod_dataform/commit/efe2c759d09cb6ccc2500bf0bb6ef0d7bc6a7fb8