An optional attribute which can be used for specifying the source of the position and size coordinates for a FIELD.
Field coordinates are fixed at the position attributes given in the IDF element tag. For backward compatibility, the shorthand for
Field coordinates are taken from an existing field in an EE fields-file, and will change if the EE field is changed using EscapeE.
If the field exists already, coordinates are taken from the EE field (like "No") but if the field does not exist in an EE fields file, the field is defined using the IDF position attributes (like "Yes").