The ID of the biopolymer chain used for fitting, e.g., A. Please note that
only one chain can be specified per instance. If all chains of a particular
structure have been used for fitting, this field can be left blank.
The ID of the biopolymer chain used for fitting, e.g., A. Please note that only one chain can be specified per instance. If all chains of a particular structure have been used for fitting, this field can be left blank.