Can retrieve the field value, but no printer can convert. it to string.
This module stores heterogeneous data defined in Schema and Field.
This module is a set of fields (Field.t and FieldRO.t) that can be addressed by their name (as string). Value can be set and retrieved as string only. However, the value itself is stored in its native type.
Create a read-only field. The returned function can be used to retrieve the value of the field.