This value of _pdbx_fraghub_investigation_screening_exp.instance_id identifiers a specific data record,
for a given experiment, in the PDBX_FRAGHUB_INVESTIGATION_SCREENING_EXP category.
For example if a fragment is characterized by "Electron diffraction it will have two data records" to have as both hit ("On-site binding") and partial-hit ("Off-site binding").